• 


. 


v 

mSm 


v  .< 


.•> 


nr  *>" 


m 
M 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


STEAM   BOILERS: 


THHE 


DESIGN,    CONSTRUCTION,    AND    MANAGEMENT. 


BY 


WILLIAM     H.     SHOCK, 

EXGINEER-IN-CHIEF,  U.  8.  N., 
CHIEF     OF     BUREAU     OF     STEAM     ENGINEERING,    U.    S.    NAVY. 


NEW   YORK : 

D.    VAN    NOSTKAND,    PUBLISHER, 

23  WAEEEX  AXB  27  MUEKAY  STREETS. 
1880. 


Copyrighted  by 

D.   VAN  NOSTRAND, 

1880. 


H.    J.   HEWITT,    PRINTER  AND   ELECTROTYPER,    27   EOSE   STREET,    NEW  YORK. 


TO  THE 

HONORABLE  R.  W.  THOMPSON, 

SECRETARY   OF   O.  S.   NAVY, 

RECOGNITION  OF  HIS  EMINENT  PUBLIC  SEBVICBS  AND  PBIVATE  WORTH, 

THIS  BOOK 

IS  RESPECTFULLY   INSCRIBED 
BY    THE    AUTHOR. 


292054 


PREFACE. 


THE  author  of  this  work  indulges  the  hope  that  he  has  in  some  degree  supplied  a 
long-felt  need  in  this  particular  branch  of  engineering  and  construction. 
His  thanks  are  due  to  Chief  Engineer  Frederick  G.  McKean  and  Passed  Assistant 
Engineer  Charles  R.  Roelker,  United  States  Xavy,  for  the  cordial  assistance  given  him 
in  its  preparation  ;  especially  to  Engineer  Roelker  for  the  great  care  and  excellent  judg- 
ment exercised  in  arranging  and  classifying  the  various  formulae  and  data  used.     He 
would  also  tender  to  Chief  Engineer  B.  F.  Ishenvood,  United  States  Navy,  his  thanks 
for  valuable  suggestions. 

In  quoting  authorities  he  has  endeavored  to  give  due  credit  where  it  belonged,  and 
any  omission  in  this  particular  is  to  be  attributed  to  unintentional  oversight. 


SYNOPTICAL    INDEX. 


CHAPTER  I. 

LSTBODTJCTOBY    EEMARKS. 

Materials  used  in  the  construction  of  boilers  in  the  early  days  of  the  steam-engine. — Eeasons 
why  copper  was  superseded  by  plate-iron. — Latest  changes  in  the  form  and  construction  of 
boilers  in  consequence  of  the  introduction  of  the  compound  engine  and  of  high  steam-pres- 
sures. 

The  essential  parts  of  a  steam-boiler  and  their  functions.  — The  form  of  boilers  may  be  varied 
almost  infinitely. — General  conditions  which  determine  the  peculiar  features  of  marine  boilers. 
— Special  conditions  affecting  the  efficiency  of  boilers  in  war-steamers. 

CHAPTER  II. 

COMBUSTION. 

Section  1. — Elementary  Constituents  of  Fuels. 

Definition  of  the  terms  combustion  and  combustibles. — Chief  combustible  constituents  of  fuels. — 
Chemical  equivalents. — Table  I.,  exhibiting  the  principal  chemical  and  physical  properties  of 
various  elementary  substances  found  in  different  fuels,  and  of  the  most  important  compounds 
resulting  from  their  combustion. 

Section  2. — Temperature  of  Ignition. 
Section  3. — Combustion  of  the  Constituents  of  Fuels. 

Combustion  of  free  carbon  forming  carbonic  acid  or  carbonic  oxide. — Combustion  of  hydro- 
carbons.— Formation  of  soot,  smoke,  and  flame. — Effect  of  the  presence  of  oxygen  and  hydro- 
gen in  fuel. — Nitrogen. — Sulphur. — Ash  and  clinker. 

Section  4. — Total  Heat  of  Combustion. 

British  thermal  unit. — Table  II.,  containing  quantities  of  heat  developed  by  combustion  of  carbon, 
hydrogen,  and  their  compounds,  and  the  weight  of  oxygen  and  of  atmospheric  air  required  for 
their  combustion. — Calorific  power  of  hydrocarbons. — Dulong's  law  of  the  calorific  power  of 
fuels. — General  formulae  for  computing  the  theoretical  calorific  power  of  fuels. — The  actual 
calorific  power  of  coals  cannot  be  determined  with  exactness  by  these  formulas. — Vaporific 
power  of  coals  in  a  steam-boiler. — W.  R.  Johnson's  experiments. 


4  SYNOPTICAL  INDEX. 

Section  5. — Fuel  as  a  Source  of  Power. 

Joule's  equivalent;.— Various  determinations  of  the  mechanical  equivalent  of  heat. — Energy  de- 
veloped by  the  combustion  of  a  pound  of  coal. 

Section  6. — Air  required  for  Combustion. 

Conditions  essential  to  the  perfect  combustion  of  a  fuel. — Formula  for  calculating  the  quantity  of 
oxygen  required  for  the  complete  combustion  of  fuels. — Weight  of  atmospheric  air  required 
for  the  combustion  of  a  pound  of  coal. — Admission  of  air  in  excess  of  the  amount  theoreti- 
cally required  for  the  complete  oxidation  of  the  fuel. 

Section  7. — Temperature  of  Combustion. 

Theoretical  calorific  intensity  of  fuels. —  Table  III.,  containing  the  theoretical  temperatures  pro- 
duced by  the  perfect  combustion  of  various  substances. — Bunsen's  experiments  on  dissociation. 
— Probable  furnace-temperatures  in  marine  boilers. 

Section  8. —  Volume  of  Products  of  Combustion. 

Volume  of  gases  of  combustion  nearly  equal  to  that  of  the  air  supplied  to  the  furnace. — Volume  of 
air. — Formula  for  calculating  the  volume  of  gises  at  different  temperatures. — Table  IV.,  ex- 
hibiting the  volumes  of  furnace-gases  per  pound  of  fuel  at  different  temperatures. 

Section  9. — Rate  of  Combustion. 

Eates  of  combustion  of  different  fuels  in  marine  boilers  with  natural  and  with  artificial  draught. — 
Bituminous  coals  compared  with  hard  anthracites  in  respect  of  rate  of  combustion. 

Section  10. — Draught  of  Furnaces. 

What  produces  the  draught  of  a  boiler. — Peclet's  formula  for  the  head  which  measures  the  draught 
of  a  boiler. — Resistances  to  the  flow  of  the  gases  of  combustion  in  the  furnace  and  flues  of  a 

boiler. — Additional  loss  of  head  in  marine  boilers. 

« 

Section  11. — Cliimney-draught. 

Head  produced  by  the  draught  of  a  chimney. — Formulae  for  calculating  the  weight,  in  pounds,  of  a 
cubic  foot  of  air  and  of  a  cubic  foot  of  chimney-gas. — Formula  for  calculating  the  unbalanced 
pressure  due  to  a  chimney  of  a  given  height. — Formula  for  calculating  the  velocity  with  which 
the  air  flows  to  the  grate  of  a  furnace. — Conclusions  drawn  from  the  latter  equation. — Practi- 
cal limits  to  the  height  and  temperature  of  the  chimney  of  marine  boilers. 

Section  12. — Artificial  Draught. 
Head  produced  by  a  blast-pipe. — Work  to  be  done  by  a  fan  or  other  blowing-machine, 

Section  13. — Efficiency  of  Furnace. 

Conditions  affecting  the  rate  of  combustion. — Regulating  the  draught  by  a  damper. — Thickness  of 
the  bed  of  fuel. — Absorption  of  heat  by  incombustible  matter  and  by  moisture  contained  in 
the  fuel. — Waste  of  unburnt  combustible  matter  in  the  solid  state. — Losses  from  an  admission 


SYXOPTICAL  IXDEX.  5 

of  excessive  quantities  of  air  to  the  furnace. — Experiment  made  by  a  board  of  United  States 
naval  engineers  to  determine  the  loss  due  to  this  cause. — Determination  of  the  loss  of  effi- 
ciency resulting  from  opening  the  furnace-doors  in  cleaning  the  fires. — Waste  of  uuburnt  fuel 
in  the  gaseous  and  smoky  states. 

Table  V.,  showing  the  character  and  efficiency  of  American  coals,  as  determined  by  W.  R.  Johnson. 

Table  VI.,  showing  the  character  and  efficiency  of  English  coals,  as  determined  by  De  la  Beche  and 
Playfair. 

Table  VI.  a,  showing  results  of  experiments  on  various  coals  of  the  carboniferous  and  cretaceous 
periods,  made  by  Chief-Engineer  B.  F.  Isherwood,  TJ.S.N. 

CHAPTER  III. 

TRANSMISSION   OF   HEAT  AND   EVAPORATION. 

Section  1. — Laics  of  Transmission  of  Heat. 

Conditions  affecting  the  quantity  of  heat  transmitted  and  the  rate  of  its  transmission. — Radiation. 
— Conduction. — Convection. — Formula  for  the  rate  of  internal  conduction  through  a  solid 
body. — Coefficients  of  thermal  resistance. — The  thermal  conductivity  of  wrought-iron  deter- 
mined by  Forbes. — Formula  for  the  rate  of  conduction  through  several  layers  of  different 
substances. — Formula  for  the  rate  of  external  conduction  between  a  solid  body  and  a  fluid. 

Section  2. — Experiments  on  the  Transmission  of  Heat,  by  B.  F.  Isherwood,  U.S.N. 

Description  of  the  manner  of  making  these  experiments. — General  results. — Thermal  conductivity 
of  copper,  brass,  wronght-iron,  and  cast-iron. 

Section  3. — Experiments  on  the  Transmission  of  Heat,  by  Peclet. 

How  the  results  obtained  by  Peclet  differ  from  those  obtained  by  Isherwood. — What  caused  this 
difference. — Peclet's  experiments  on  the  cooling  of  vessels  exposed  to  the  air. 

Section  4. — Transmission  of  Heat  in  a  Steam-boiler. 

Evaporative  power  of  the  heating-surfaces  in  a  steam-boiler. — Rankine's  approximate  formula  for 
the  quantity  of  heat  transmitted  by  the  heating-surfaces  of  a  boiler. — Circulation  of  the  water 
in  boilers. — Heat-absorbing  capacity  of  water. 

Section  5. — Efficiency  of  Heating-surfaces  in  a  Steam-boiler. 

Measure  of  the  efficiency  of  hea'ing-snrfaces. — Conditions  affecting  the  efficiency  of  heating-sur- 
faces.— Armstrong's  experiment  on  the  efficiency  of  heating-surfaces. — Differences  of  tempe- 
rature in  a  steam-boiler. — Transmission  of  heat  through  the  plates  forming  the  furnace  and 
the  combustion-chamber. — Radiation  of  heat  from  incandescent  carbon. — Evaporation  from 
the  heating-surfaces  of  the  furnaces  and  back-connections  of  return-tube  boilers,  determined 
by  Isherwood. — Evaporation  from  the  heating-surfaces  of  tubes. — Differences  of  temperature 
of  gases  discharged  from  the  upper  and  lower  rows  of  horizontal  fire-tubes. 


6  SYNOPTICAL  INDEX. 

Section  G. — Loss  of  Efficiency  of  Boilers  by  External  Radiation  and  Conduction. 

The  loss  of  heat  by  radiation  from  the  furnace  and  from  the  chimney  is  trifling. — Experiments  on 
the  loss  of  heat  by  radiation  and  conduction  from  steam-boilers,  pipes,  etc.,  protected  by  dif- 
ferent thicknesses  of  felting. — Experiments  to  determine  the  effect  of  covering  the  boiler  with 
felt  on  the  economic  evaporation,  made  at  the  Navy- Yard,  New  York,  in  1863 

Section  7. — Efficiency  of  Boilers. 

Measure  of  the  efficiency  of  boilers. — Heat  expended  in  the  production  of  chimney-draught. — 
Rankine's  formula  for  the  efficiency  of  boilers. 

Section  8. — Influence  of  the  Rate  of  Combustion  on  the  Evaporative  Efficiency  of  Boilers.  (From 
"Experimental  Researches,"  Vol.  II.,  by  Chief-Engineer  B.  P.  Isherwood,  U.S.N.) 

Table  VII ,  showing  the  economical  and  potential  evaporation  of  the  horizontal  fire-tube  boiler 
with  anthracite  consumed  with  different  rates  of  combustion. 

Section  9. — Superheated  Steam. 

Drying  and  superheating  steam. — Tute  and  Fairbairn's  experiments  on  the  density  of  superheated 
steam.—  Increase  of  the  dynamic  efficiency  of  steam  in  the  engine  by  drying  and  superheating. — 
Results  of  Isherwood's  experiments  with  superheated  steam. — TT.S.S.  Mackinaw. — U.S.S. 
Eutaw. — Steamer  Georgeanna. — Practical  limits  to  the  degree  of  superheating. 

Section  10. — Efficiency  of  Superheating  Surfaces. 

Superheating  surfaces  in  a  boiler. — Different  methods  of  superheating  steam. — Relative  economic 
value  of  water-heating  and  superheating  surfaces  in  marine  boilers. — Value  of  superheaters 
practically  considered. 

Table  VIIL,  showing  properties  of  water  and  steam. 


CHAPTER  IV. 

MATERIALS. 

Section  1. — Relative  Value  of  Materials  for  Bt>iler  Construction. 
Section  2. — Copper. 

Advantages  and  disadvantages  connected  with  the  use  of  copper  as  a  material  for  boilers. — Present 
use  of  copper  in  boiler-making. 

Section  3. —  Composition. 
General  character. — Brass. — Brass  boiler-tubes.— Bronze. — Phosphor-bronze. 

Section  4. — Tenacity  of  Metals  at  Various  Temperatures. 

Experiments  made  at  Portsmouth  Dockyard,  England.— Table  IX.,  showing  tenacity  of  various 
metals  at  different  temperatures  up  to  500°  Fahr. 


SYNOPTICAL  INDEX.  7 

Section  5. — Cast-iron. 
Section  6. —  Wrought-iron. 
Its  use  in  boiler-making. — Qualities  which,  it  must  possess  for  this  purpose. 

Section  1. — Brands  of  Plate- iron  used  in  Boiler-making. 

American  charcoal-irons. — Shell-iron. — Flange-iron. — Firebox-iron. — Special  brands  of  boiler-iron. 
— Sizes  of  boiler-plates. — English  boiler-iron. 

Section  8.— Steel. 

Processes  of  manufacture. — Qualities  of  mild  steel  used  in  boiler-making. — Steel  compared  with 
wrought-iron. — Tenacity  of  steel  boiler-plates. — Effects  of  severe  strains  and  of  corrosion. — 
Extracts  from  a  report  by  the  surveyors  to  Lloyd's  Registry  on  the  use  of  steel  for  boilers. 

Table  X.,  exhibiting  certain  physical  and  mechanical  properties  of  various  metals. 

Table  XI..  weight  of  wrought-iron  plates  and  bars  (square  and  round). 

Table  XII.,  weight  of  flat  bar-iron  per  foot. 

Table  XIII.,  weight  of  sheet  and  plate  iron. 

Table  XIV.,  weight  of  wrought  angle-iron. 

Table  XV.,  weight  of  wrought  T-iron. 

Table  XVI.,  wrought-iron  bolts  with  square  heads  and  nuts. 

Table  XVII.,  standard  sizes  of  washers. 

Table  XVIII.,  showing  number  of  Burden's  rivets  in  100  pounds. 

CHAPTER  V. 

TESTING   THE   MATERIALS. 

Section  1. — General  Character  of  Tests. 

Section  2. —  United  States  Laics  and  Regulations  regarding  the  Tests  of  Boiler-plates. 
United  States  Revised  Statutes,  sec?.  4430  and  4431. — Rules  3  and  4  of  General  Rules  and  Regu- 
lations prescribed  by  the  Board  of  Supervising  Inspectors  of  Steam  Vessels,  1879. 

Section  3.  —  The  Rodman  Testing-machine. 

Description  of  the  testing-machine  at  the  Ordnance  Department  of  the  Navy- Yard,  Washington, 
D.  C. — Manner  of  making  tests  with  this  machine. 

Section  4. — Form  and  Dimensions  of  Tent-specimens. 

Sectional  area. — Length. — Form. — Experiments  on  the  influence  of  length  and  form  on  the  appa- 
rent strength  of  specimens. — Care  to  be  taken  in  preparing  specimens. 

Section  5. — Effects  produced  by  Stress. 

Rate  of  elongation  of  wrought-iron  under  a  tensile  stress. — The  interior  and  exterior  portions  of  a 
wrought-iron  bar  not  in  equilibrium.— Stretching  of  ductile  and  fibrous  materials. — Flow  of 
solids. 


8  SYNOPTICAL  INDEX. 

Section  6. — Experiments  on  the  Effects  of  Hammering  and  Rolling  on  the  Strength  of  Bars. 

Results  deduced  from  experiments  by  the  U.  S.  Test- Board.—  Table  XIX.,  showing  the  effect  of 
variation  and  of  uniformity  in  the  rate  of  reduction  from  pile  to  bar  on  the  tensile  strength 
and  the  elastic  limit  of  wrought-irou  bars. — Experiments  made  by  Chief-Engineer  William  H. 
Shock,  U.S.N.,  on  the  influence  of  hammering  and  rolling  on  the  tenacity  and  ductility  of  a 
wrought-iron  bar. 

Section  7. — Appearance  of  Fractures. 

Quality  of  iron  and  steel  bars  indicated  by  the  appearance  of  their  grain  or  fibre  when  fractured. — 
Appearance  of  the  same  bar  may  be  changed  by  altering  the  manner  of  fracturing  it. 

Section  8. — Hot  and  Cold  Forge-tests. 
Forge-tests  applied  to  boiler-plates. — Applying  the  bending-test  to  plates. — Testing  rivets. 

Section  9. — Directions  for  Testing  Bar-iron. 
Section  10. — Testing  Steel  Boiler-plates  (French  Government  tests). 

Section  11. — Tests  for  Plate,  Beam,  Angle,  Bulb,  and  Bar  Steel  used  in  Building  Ships  for  Her 

Majesty's  Navy  (Admiralty,  9th  January,  1879). 

Section  12. — Examining  Boiler-plates. 
CHAPTER  VI. 

PEINCIPLES   OF   THE   STRENGTH   OF   BOILERS. 

Section  1. — Resistance  of  Spherical  Shells  to  an  Internal  Fluid  Pressure. 

Stress  produced  by  an  internal  fluid  pressure. — Strength  of  thin  spherical  shells. — Stress  in  thick 
spherical  shells. 

Section  2. — Resistance  of  Cylindrical  Shells  to  an  Internal  Fluid  Pressure. 

Stress  in  a  longitudinal  direction. — Stress  in  a  tangential  direction. — End-attachment  of  cylindri- 
cal shells. — Navier's  experiment  on  strength  of  wrought-iron  shells. 

Section  3. — Resistance  of  Cylindrical  Shells  to  an  External  Fluid  Pressure. 

Fairbairn's  formula. — Table  XX.,  containing  the  2.19th  power  of  several  numbers. — Belpaire's  in- 
vestigation of  the  collapsing  strength  of  flues. — Table  XXI.,  containing  numerical  values  for 
factor  S  of  Belpaire's  formula. — Grashof's  formula. 

Section  4. — Experiments  made  on  the  Resistance  of  Cylindrical  Flues  to  an  External  Fluid  Pressure. 

Description  of  apparatus  used  in  experiments  made  at  the  Navy- Yard,  Washington,  D.  C.,  in  1874. 
—Results  of  experiments. — Application  of  Fairbairn's  and  Belpaire's  formulae  to  these  expe- 
riments. 


SYNOPTICAL  INDEX.  9 

Section  5.—  Strength  of  Flat  Plates. 

Investigation  of  the  strength  and  stiffness  of  flat  plates. — Formulae  for  calculating  the  strength  of 
unstayed  flat,  circular,  rectangular,  and  square  plates. — Stiffness  of  flanged  flat  plates. — 
Stiffness  of  buckled  plates. 

Section  6. — Strains  on  Braces  and  their  Attachments. 
Perpendicular  braces. — Oblique  braces. — Strains  in  a  system  of  oblique  braces. 

Section  7. — Strains  on  Circular  Arcs. 
CHAPTER  VII. 

DESIGN",    DBAWINGS,    AND   SPECIFICATIONS. 

Section  1. — General  Considerations  governing  the  Design  of  Marine  Sailers. 

Section  2. — Boiler  Power. 

Relative  evaporative  efficiency. — Actual  power  of  a  boiler. — Consumption  of  steam  in  marine 
engines. — Number  of  indicated  horse-powers  per  square  foot  of  grate. 

Section  3. —  Various  Types  of  Marine  Boilers. 

Various  forms  of  boiler-shelK — Water-tube  and  fire-tube  boilers. — Rectangular  boilers  of  United 
States  naval  vessels. — Boiler  of  U.S.S.  Lacka wanna. — Rectangular  boilers  with  two  tiers  of 
furnaces. — Arrangement  of  tubes  in  oval  and  circular  shells. — Size  and  number  of  furnaces  in 
cylindrical  boilers. — Cylindrical  boiler  with  the  tubes  arranged  at  the  sides  of  a  single  furnace. 
— Double-end  cylindrical  boiler. — Boiler  of  U.S.S.  Daylight. — Boiler  of  U.S.S.  Mahaska. — Lo- 
comotive types  of  boiler  designed  for  marine  and  railroad  purposes. — Vertical  fire-tube  boiler. 
— Dickerson's  marine  boiler. 

Table  XXII.,  showing  the  dimensions,  proportions,  and  weights  of  boilers  of  various  types. 

Table  XXIII.,  showing  the  economic  evaporation  of  boilers  of  various  types  under  different  con- 
ditions. 

Section  4. — Space  and  Weight  required  for  Boilers  of  a  Given  Power. 

Relative  proportions  of  weight  and  space  required  for  boiler,  fire-room,  and  fuel. — Solution  of  the 
problem  for  a  given  horizontal  fire-tube  boiler. — Determination  of  the  best  rate  of  combustion 
for  the  given  boiler. — Table  XXIV.,  exhibiting  the  space  and  weight  required  with  the  hori- 
zontal fire-tube  boiler,  having  a  rectangular  shell  and  the  tubes  arranged  above  the  furnaces, 
and  with  anthracite  with  one-sixth  refuse,  to  furnish  a  given  supply  of  steam  per  hour  for  200 
hours,  with  different  rates  of  combustion. 

Section  5. — Proportioning  the  Parts  of  a  Boiler. 

Length  and  width  of  the  grate. — Ashpit. — Furnace. — Calorimeter  over  the  bridge-wall. — Back- 
connection. — Calorimeter  through  or  between  the  tubes. — Calorimeter  of  the  chimney.— Heat- 
ing-surface.— Water-spaces. — Water  and  steam  room. 


10  SYNOPTICAL  INDEX. 

Section  6. — Relative  Value  of  Various  Forms  for  Boiler  Construction. 
Spherical  shell. — Cylindrical  form. — Flat  surfaces. 

Section  7. — Factor  of  Safety. 

Factor  of  safety  variable. — Allowance  for  corrosion. — Stiffness  of  stayed  surfaces. — Limit  of  high- 
est working  pressure. — Strains  in  consequence  of  variations  of  temperature. — Factor  of  safety 
for  steel  boiler-plates. — Section  4433  of  United  States  Revised  Statutes. — Factor  of  safety  of 
flues  subjected  to  compression. — Stays  and  braces. 

Section  8. — Drawings  and  Specifications. 

Section  9. — Specifications  for  Sailers  of  U.S.S.  "  Lackawanna." 

Section  10. — Extract  from  Specifications  for  Engines  of  U.S.S.  "  Miantonomoh." 

Section  11. — Specifications  of  Boilers  (Iron  Shells)  for  Vessels  of  the  English  Navy. 

Section  12.— Material  for  Six  Boilers  of  U.S.S.  "  Nipsic." 
Section  13.— List  of  Steel  and  Iron  Plates,  Rivets,  Tubes,  etc.,  for  Boiler  of  Steamer  "  Lookout." 

CHAPTER  VIII. 

LAYING-OFF,  FLANGING,  RIVETING,  WELDIN.G,  ETC. 

Section  1. — Laying-off. 

Levelling  plates. — Marking  lines  and  rivet-holes. — Laying-off  the  front-head  and  tube-sheet  of  the 
boilers  for  U.S.S.  Nipsic. — Finding  the  length  of  plates  for  a  cylindrical  shell  with  butt-joints. 
—Laying-off  a  cylindrical  shell  or  flue  formed  of  alternate  inner  and  outer  rings  with  lap-joints- 
—Laying-off  plates  for  conical  tubes. — Laying-off  a  cylindrical  shell  or  flue  formed  of  rings 
lapping  telescopically. — Laying-off  plates  for  a  cylindrical  shell  with  a  wedge-shaped  portion 
cut  off. — Laying-off  plates  for  the  cylindrical  shell  of  a  steam-dome. 

Section  2. — Shearing  and  Planing. 

Cutting  openings  for  manholes,  furnaces,  etc.,  in  boiler-plates. — Shearing-machine. — Relative  ad- 
vantages of  shearing  and  planing. 

Section  3. — Bending. 
Arrangement  of  bending-rolls. — Bending  plates  to  a  circular  shape. 

Section  4. — Flanging. 

Bending  plates  cold. — Flanging  iron  and  steel  plates. — Practical  instructions  regarding  flanging. — 
Circular  flanges. 

Section  5. — Punching. 

Process  of  punching  plates.— Forms  of  punches.— Kennedy's  helical  punch.— Sizes  of  punch  and 
die. — Power  required  to  punch  steel  plates. — Plates  to  be  punched  from  the  faying  sur- 
faces.—Form  of  punched  holes.— Loss  of  tenacity  due  to  punching. 


SYNOPTICAL  INDEX.  11 

Section  6. — Drilling. 

Precautions  in  drilling  boiler-plates. — Drilling  compared  with  punching. — Harvey's  boiler-drilling 
machine. — Method  of  drilling  plates  of  cylindrical  boilers  of  U.S.S.  Galena. 

Section  7. — Riveting. 

Half-blind  rivet-holes. — Drifting. — Operation  of  hand-riveting. — Effect  of  percussion  on  the 
strength  of  iron  and  steel.— Steam  and  hydraulic  riveting  machines. — Hand-riveting  and  ma- 
chine-riveting compared. — Steam  riveting-machine  of  the  Providence  Steam-Engine  Company, 
Providence,  R.  I. — Tweddell's  hydraulic  machine  tools. — Stationary  and  portable  hydraulic 
riveting-machines. — Number  of  rivets  driven  per  day's  work. — Cold  riveting. — Steel  rivets. 

Section  8. — Forms  of  Rivets. 

Dimensions  of  a  f-inch  rivet. — Forms  of  rivet-points. — Table  XXV.,  giving  lengths  of  shank  re- 
quired to  form  different  rivet-points. — Snap  points. — Conical  points. — Countersunk  rivets. 

Section  9. — Stylts  of  Joints. 
Section  10. — Friction  in  Riveted  Joints. 

Reed's  experiments  to  determine  the  amount  of  friction  in  riveted  joints. — Friction  in  its  relation 
to  the  strength  of  riveted  joints. — Causes  tending  to  diminish  the  friction  of  riveted  joints. 

Section  11. —  Straining  Action  on  Riveted  Joints. 

Conditions  producing  the  strongest  joints. — Apparent  breaking  stress  defined. — Unequal  distribu- 
tion of  stress  due  to  eccentricity  of  load. — Local  action  of  contiguous  material. — Influence  of 
holes  on  distribution  of  stress  and  on  the  apparent  strength  of  plates. — Strained  zones  around 
punched  holes. — Excessive  crushing  action  between  rivets  and  plates. — Stress  in  multiple- 
riveted  joints  of  materials  of  different  elasticities. 

Section  12. — Strength  of  Materials  in  Riveted  Joints. 

Loss  of  tensile  strength  in  riveted  iron  and  steel  plates  due  to  punching. — Shearing  strength  of  iron 
and  steel  rivets  according  to  W.  R.  Browne,  Fairbairn,  David  Greig,  and  Max  Eyth. — Formula 
expressing  relation  between  crushing  pressure  and  shearing  resistance  of  rivets. — Limit  of 
crushing  pressure  in  riveted  joints. — Maximum  crushing  pressure  of  the  rivets  on  the  plate. — 
Influence  of  crushing  pressure  on  apparent  tenacity  of  riveted  plates. — Probable  influence  of 
the  relative  hardness  of  the  rivets  and  plates. 

Section  13. — Proportioning  Riveted  Joints. 

Different  modes  of  fracture  of  riveted  joints. — Elements  affecting  the  efficiency  of  riveted  joints. — 
Formula  for  finding  the  diameter  of  rivets  for  a  given  thickness  of  plate,  with  the  rivets  in 
single-shear  and  in  double-shear. — Usual  practice  in  proportioning  the  diameter  of  rivets  to 
the  thickness  of  plates  for  iron  plates,  and  for  steel  plates. — Width  of  lap. 

Section  14. — Lap-joint*. 
Single-riveted  lap-joint. — Its  characteristic  features. — Formula  for  finding  the  pitch  of  rivets. 


12  SYNOPTICAL  INDEX. 

Double-riveted  lap-joint. — Formula  for  finding  the  pitch  of  rivets. — Zigzag  riveting. — Chain-rivet- 
ing. 
Treble  and  quadruple  riveted  lap-joints. 

Section  15. — Experiments  on  the  Strength  of  Lap-joints. 

Fairbairn's  experiments. — Eeasons  why  Fairbairn's  conclusions  regarding  the  strength  of  riveted 
joints  cannot  be  accepted  as  trustworthy. — Experiments  by  W.  Bertram  published  and  dis- 
cussed by  D.  K.  Clark. — Decrease  of  the  apparent  tenacity  of  riveted  lap-joints  as  the  thickness 
of  plates  increases. — Mean  results  of  experiments  with  single-riveted  joints. — Loss  of  apparent 
tenacity  of  joints  with  punched  and  drilled  holes. — Mean  shearing  resistance  of  rivets. — Mean 
efficiency  of  single-riveted  joints. 

Mean  apparent  tenacity  and  efficiency  of  double-riveted  joints. — R.  V.  J.  Knight's  experiments  with 
double-riveted  joints  made  of  ^-inch  and  1-inch  punched  iron  plates. — Average  results  of  ex- 
periments with  double-riveted  steel  plates. 

Experiments  by  Kirkaldy  on  treble  and  quadruple  riveted  steel  plates. — Table  XXVI.,  results  of 
experiments  with  treble  and  quadruple  riveted  lap-joints,  steel  plates.  Tested  by  Kirkaldy. 

Table  XXVII.,  proportions  of  single-riveted  joints. 

Table  XXVII  a,  French  practice  in  single-riveted  joints. 

Table  XXVIII.,  proportions  of  double-riveted  lap-joints. 

Section  16. —  Various  Forms  of  Lap-joints. 

Single-riveted  diagonal  lap-joint. — Single-riveted  joint  with  oval  rivets. — Single-riveted  lap-joint 
with  covering-plate. — Plates  with  thickened  edges. 

Section  17. — Butt-joints. 

Single-welt  butt-joint. — Double-welt  butt-joints. — Formulae  for  finding  the  pitch  of  rivets  in  single- 
riveted  and  double-riveted  double-welt  butt-joints. — Proportions  of  single-riveted  double-welt 
butt-joints  according  to  the  practice  of  the  Crewe  Works  (England). — Modified  proportions 
when  double-welt  butt-joints  and  lap-joints  occur  on  the  same  plate. —  Table  XXIX.,  Wilson's 
table  of  proportions  of  double-riveted  butt-joints  with  two  covering-plates. 

Table  XXX.,  Kirkaldy's  experiments  on  the  comparative  strength  of  chain  and  zigzag  riveting  in 
double-welt  butt-joints. 

Table  XXXI.,  strength  of  rivet- work  in  single  and  double  riveted  lap  and  butt-joints,  with  drilled 
and  punched  plates. — Experiments  with  chain  and  zigzag  riveted  double-welt  butt-joints,  steel 
plates  and  steel  rivets . 

Table  XXXII.,  results  of  experiments  with  single  and  double  riveted  double-welt  butt-joints. 

Section  18. —  Calking. 

Method  of  calking  the  lap-edges  of  joints. — Ordinary  calking- tool.— Connery's  calking-tool. — Calk- 
ing the  butts  of  plates. — Precautions  to  be  observed  in  calking. 

Section  19. —  Welding. 

Definition  of  welding. — Defective  welding  due  to  the  presence  of  oxide  of  iron. — Effect  of  chemical 
composition  on  the  welding  of  iron. — A.  L.  Holley  on  welding  iron. 


SYNOPTICAL  INDEX.  13 

Section  20. —  Welding  Boiler-plates. 

Bertram's  method  of  welding  boiler-plates. — Scarf-weld. — Lap-weld. — Welded  seam  with  covering- 
plate. — Welding  furnace-flues. — Welding  the  longitudinal  seams  of  a  cylindrical  boiler-shell. — 
Welding  the  front  plates  of  a  boiler. — Welding  angle-iron  rings. — Practical  suggestions  con- 
cerning welding. — Difficulties  connected  with  the  welding  of  plates. 

Section  21. — Strength  of  Welded  Plates. 

Results  of  experiments  on  the  tensile  strength  of  welded  joints  recorded  by  Kirtley. — Experiments 
on  the  strength  of  welded  joints  by  Gillott. 

CHAPTER  IX. 

SHELL,  FURNACES,  AND  BACK- CONNECTIONS. 

Section  1. —  Various  Forms  of  Shells. 

C.  E.  Emery's  connected-arc  marine  boiler. — Thickness  of  cylindrical  plates. — Thickness  of  flat 
plates. — Stiffening  plates  around  manholes. — Quality  of  iron  for  boiler-shells. 

Section  2. — Rectangular  Shells. 

Rectangular  boilers  of  IT.  S.  naval  vessels. — Thickness  of  plates. — Manner  of  connecting  the  plates. 

Section  3. — Cylindrical  Shells. 

Manner  of  building  up  cylindrical  shells. — Back  and  front  heads. — Lloyd's  rules  for  determining 
the  strength  of  circular  shells. — Rules  of  the  surveyors  of  the  Board  of  Trade  (England)  for 
determining  the  strength  of  cylindrical  shells. 

Section  4. — Furnaces. 

General  arrangement  of  seams,  laps,  and  braces  on  furnaces. — Quality  of  iron  for  furnaces. — Use 
of  steel  and  copper  for  furnaces. — Corrugated  furnace-flues. 

Section  5. — Furnaces  of  Rectangular  Boilers. 

Circulation  of  water  with  flat  and  arched  furnace-crowns. — Relative  advantages  of  various  forms  of 
furnace- oro WQB. — Manner  of  securing  furnaces  to  the  front  of  boilers  and  to  the  back-connec- 
tions.— Furnace  of  a  marine  tubular  boiler  built  by  Laird  &  Son,  Birkenhead,  England. — 
Furnace  for  a  boiler  of  the  U.  S.  Tugboat  Glance. — Manner  of  securing  furnaces  to  the  shell 
when  the  water-spaces  are  narrow. — Usual  method  of  securing  furnaces  in  rectangular  boilers 
of  U.  S.  naval  vessels. — Water-bottoms. — Water-legs  of  dry-bottom  boilers. 

Section  6. — Cylindrical  Furnaces. 

Construction  of  cylindrical  furnaces. — The  Adamson  joint. — T-iron  rings  for  furnace-flues. — The 
Bowling  hoop. — Directions  regarding  the  application  of  strengthening-hoops  to  furnace-flues. 
— Manner  of  securing  furnace-flues  to  the  boiler-shell. — Description  of  furnaces  of  boiler  illus- 
trated on  Plate  XV. — Rules  of  Lloyd's  and  of  the  Board  of  Trade  (England)  for  the  strength 
of  circular  flues. 


14:  SYNOPTICAL  INDEX. 

Section  7. — Combustion-chambers  and  Back-connections. 

Combustion-chamber  in  various  type8  of  boilers. — Bridge- walls. — Arrangement  of  back-connections. 
— Construction  of  back-connection  in  horizontal  tubular  and  vertical  return-tube  boilers. 

Section  8. — Systems  of  Boiler-building. 

General  rules  observed  in  boiler-building. — Method  pursued  in  building  the  cylindrical  boiler  repre- 
sented on  Plate  XII. — Building  rectangular  boilers. 

CHAPTER  X. 

STAYS  AND  BRACES. 

Section  1. — Systems  of  Bracing. 

Surfaces  to  which  bracing  has  to  be  applied. — Methods  of  staying  and  bracing. — Spacing  of  braces. 
—Various  devices  in  bracing  to  keep  the  interior  of  the  boiler  accessible. — Care  required  to 
prevent  distortion  of  plates  to  which  braces  are  attached. — System  of  bracing  in  cylindrical 
boilers. — System  of  bracing  in  rectangular  boilers  of  U.  S.  naval  vessels. — Bracing  in  English 
horizontal  return-tube  boilers. — Bracing  in  horizontal  return-tube  boilers  of  U.S.S.  Tippeca- 
noe. — System  of  bracing  in  rectangular  boilers  of  French  naval  vessels. 

Section  2. — Rules  for  Proportioning  Braces. 

Area  of  plate  supported  by  a  brace. — Factor  of  safety. — Corrosion  of  braces. — Lloyd's  rules  for 
determining  the  strength  of  stays  and  flat  plates. — Board  of  Trade's  (English)  rules  for  deter- 
mining the  strength  of  stays  and  flat  plates. — Weisbach's  formula  for  the  thickness  of  flat 
stayed  plates. — Eatio  of  diameter  of  stays  to  thickness  of  plate. — Gussets. — Girder-stays. — For- 
mulae for  the  strength  and  depth  of  girder-stays. — Board  of  Trade's  (English)  rule  for  finding 
the  strength  of  girder-stays. — Rankirie's  rules  for  the  strength  of  easy-fitting  and  tight-fitting 
fastenings  of  braces. — Bearing-surface  of  connecting-pins  or  bolts. — Experiments  by  Charles 
Fox. 

Section  3. — Screw-stays  and  Socket-bolts. 

General  arrangement  and  relative  advantages  of  various  forms  of  stay-bolts  and  rivets. — Sockets. — 
Screw-stays. 

Section  4. —  Various  Forms  of  Stays  and  Modes  of  Fastening  Them. 

Stay  used  in  narrow  water-spaces  of  French  boilers. — Staying  the  vertical  sides  of  tube-boxes  or 
back-connections  by  lugs  and  pins. — Form  of  stay  used  in  boilers  of  U.S.S.  Lancaster. — Short 
stays  connecting  surfaces  that  are  not  parallel. — Forked  stays. — Triangular  stays  attached  to  the 
lower  rounded  corners  of  furnaces. — Stay-rods  secured  by  nuts  and  washers. — Staying  the  flat 
ends  of  cylindrical  boilers. — Rod-braces  of  boilers  of  U.S.S.  Terror. — Do.  of  U.S.S.  Amphitrite. 
— Do.  of  U.S.S.  Miantonomoli. — Do.  of  a  boiler  built  by  R.  Napier  &  Co.,  Glasgow. — Braces 
with  T-ends. — Flexible  braces. — Braces  of  boilers  of  U.S.S.  Monadnock. — Eye-bars. — Braces 
with  oblique  branches. — Attachment  of  braces  to  adjacent  furnace-crowns  by  triangular  links 
and  frames. — Cheap  forms  of  branch -braces. — Bolts  and  split  pins. — Adjustable  braces. 


SYNOPTICAL  INDEX.  15 

Section  5. — Fitting  and  Adjusting  Rod-braces. 

Forging  braces. — Forming  the  ends  of  braces. — Flat  braces. — Sagging  of  long  braces. — Setting-up 
braces. 

Section  6. — Girder-stays,  Gusset-stays,  Stay-plates,  Stay-domes,  etc. 

Various  forms  of  girder-stays. — Stay  for  front  plate  of  back-connection  of  boilers  of  U.S.S.  Mian- 
tonomoh  and  class. — Staying  flat  surfaces  with  angle  and  T-irons. — Gusset-plates. — Stay-domes. 

Section  7. — Experiments  on  the  Shear  ing -strength  of  Wrought-iron  Bolts. 

Section  8. — Experiments  made  to  Determine  the  proper  Dimensions  of  Pins,  Eyes,  and  Shanks  of 

Boiler-braces. 

Section  9. — Experiments  on  Screw  Stay-bolts. 
CHAPTER  XI. 

FLUES  AXD  TUBES. 

Section  1. — Flue-boilers. 

Early  flue-boilers. — Return-flue  boilers. — Drop-flue  boilers. — Galloway  tubes. — Lamb  and  Sumner 
boilers. 

Section  2. — Relative  Advantages  of  Flues  and  Tubes  for  Marine  Boilers. 
Section  3. —  Various  Types  of  Tubular  Boilers. 

Arrangement  of  tubes. — Considerations  governing  the  arrangement  and  location  of  tubes  in  marine 
boilers. 

Section  4. — Dimensions  and  Spacing  of  Tubes. 

Conditions  governing  the  dimensions  and  spacing  of  tubes. — Vertical  water-tubes. — Tubes  of  boiler 
of  U.S.S.  Lackau-anna. — Arrangement  of  vertical  water-tubes  in  zigzag  rows. — Diameter  and 
length  of  fire-tubes. — Spacing  of  horizontal  fire-tubes. — Stimer's  differential  tubular  boiler. — 
Ferruling  and  swaging  tubes. 

Section  5. — Iron,  Steel,  Brass,  and  Copper  Tubes. 

Relative  advantages  of  boiler-tubes  made  of  different  materials. — Lap-welded  iron  tubes  and  seam- 
less drawn  brass  tubes.— Experiments  with  boiler  of  U.S.S.  Wyoming. — Steel  tubes. — Draw- 
ing tubes. — Tapering  tubes. 

Talle  XXXIII.,  sizes  and  weights  of  lap-welded  iron  boiler-tubes  of  standard  gauge  manufactured 
by  the  National  Tube-Works  Company. 

Table  XX  XIV.,  standard  dimensions  of  lap-welded  American  charcoal-iron  boiler-tubes  manu- 
factured by  Morris,  Tasker  &  Co. 

Table  XXXV.,  regular  sizes  and  weights  of  seamless  drawn  brass  and  copper  tubes,  manufactured 
by  the  American  Tube- Works,  Boston,  Mass. 

Table  XXXVI.,  Stub's  wire-gauge. 


16  SYNOPTICAL  INDEX. 

Section  6. — Methods  of  Expanding  Tubes. 

Ordinary  method  and  process  of  securing  tubes  in  the  tube-plates  by  expanding  their  ends. — Ray- 
mond's  patent  recessed  tube-sheet. — Prosser's  expanding-tool. — Dudgeon's  tube-expander. — 
TweddelPs  hydraulic  tube-expander. — Kiveting  over  the  tube-ends. — Selkirk's  tube-beader. — 
Precautions  to  be  taken  in  expanding  tubes. 

Section  7. — Stay -tubes. 

Stay- rods  for  tube-plates  unnecessary. — Stay-tubes  of  boilers  for  U.S.S.  Nipsic. — English  practice. 
— Stay-tubes  for  boilers  of  steamer  Atrato,  built  by  James  Watt  &  Co. — Stay-tubes  for  boilers 
of  steamer  Lord  of  the  Isles. 

Section  8. — Devices  for  Rendering  Boiler-tubes  Removable. 

Removing  tubes  secured  by  expanding  their  ends. — French  iron  boiler-tubes. — Removable  tubes  in 
boilers  built  at  the  West  Point  Foundry,  Cold  Spring,  N.  Y. — Pauksch's  boiler-tubes. — Re- 
movable tubes  used  in  French  naval  boilers ;  viz.,  systeme  Internet  et  Gouttes,  systeme  Toscer, 
and  systeme  Langlois. — Removable  tubes  used  in  some  United  States  naval  boilers. 

Section  9. — Experiments  on  the  Holding-power  of  Boiler -tubes  secured  by  various  Methods. 
Section  10. — Sectional  or  Water-tube  Boilers,  Hanging-tubes,  Double-tubes,  etc. 

General  character  of  stationary  water-tube  boilers. — Principal  advantages  claimed  for  these  boilers. 
— Failure  of  attempts  to  use  these  boilers  on  board  of  vessels. — Perkins  tubulous  boiler. — 
Howard  marine  water-tube  boiler. — Belleville  water-tube  boiler  for  despatch  vessel  L' Active. 
— Herreshoff  coil-boiler  of  the  steam-yacht  Estelle. — Performance  of  the  Herreshoff  coil-boiler. 
— Davey-Paxman  boiler. — Hanging  tubes. 

CHAPTER  XII. 

UPTAKE,    CHIMNEY,    STEAM-JETS,   FAN-BLOWEES,   ETC. 

Section  1. — Smoke-connections  and  Uptake. 

General  form  and  arrangement  of  smoke-connections. — Front  smoke-connections  and  uptakes  of 
rectangular  boilers. — Front  smoke-connections  and  uptakes  of  cylindrical  boilers. — Front-con- 
nections and  uptake  of  boilers  of  U.S.S.  Nipsic. — Front-connections  and  uptake  of  boilers  of 
U.S.S.  Trenton. — Importance  of  making  uptakes  and  their  doors  air-tight. 

Section  2. — Forms  and  Dimensions  of  Chimneys. 

Chimneys  of  circular  and  oval  cross-section. — Subdividing  the  cross-area  of  chimneys  by  partitions. 
— Dimensions  of  chimneys. — Telescopic  chimneys  for  war-vessels. — Friction  of  gases  in  and 
radiation  of  heat  from  chimneys. — Damper. 

Section  3. — Fixed  Chimneys. 

Construction  of  fixed  chimneys. — Manner  of  securing  them  to  uptake. — Chimney-stays. — Casing. — 
Water-tank  in  hatch. — Chimney  for  U.S.S.  Algoma  and  class. 


SYNOPTICAL  INDEX.  17 

Section  4. — Hoisting  Chimneys. 

Hoisting  chimney  illustrated  by  Ledieu. — Chimney  of  U.S.S.  Plymouth. — Hoisting-gear  for  chim- 
neys.— Chimney  of  U.S.S.  Nipsic. — Double-hoist  and  single-hoist  chimneys  compared. — Chim- 
ney of  U.S.S.  Quinnebaug  and  class. 

Section  5. — Artificial  Draught :  Blast-pipe,  Steam-jets,  Fan-blowers. 

Artificial  compared  with  natural  draught. — Efficiency  of  mechanism  for  producing  artificial  draught 
— Various  methods  of  producing  artificial  draught. — Action  of  fluid-on-fluid-impulse  machines. 
— Blast-pipe  of  locomotives. — Steam-jets. — Jet-arrangement  for  chimney  of  U.S.S.  Algoma 
and  class. — Fan-blowers. — Air-tight  fire-room. — Koerting's  jet-apparatus. 

Section  6. — Experiments  with  Artificial  Draught  in  Marine  Boilers. 
Experiments  made  at  the  U.  S.  Nary- Yard,  New  York,  1865-66. 

Table  XXXYIL,  showing  results  of  experiments  made  at  the  Navy- Yard,  New  York,  in  the  years 
1865-66,  with  various  devices  for  producing  artificial  draught  in  marine  boilers. 

CHAPTER  XIII. 

STEAM-BOOM   AND  SUPERHEATERS. 

Section  1. — Capacity  of  Steam-room. 

Influence  of  capacity  of  steam-room  on  the  efficiency  of  the  engine. — Bourne  on  the  capacity  of 
marine  boilers. — Capacity  of  steam-room  in  French  naval  boilers. — Height  of  steam-room. 

Section  2. — Steam-drums. 

Form  and  arrangement  of  steam-drams. — Weakening  effect  of  steam-domes  built  on  cylindrical 
shells,  and  methods  of  strengthening  them. 

Section  3. — Superheaters. 

Superheating  surface  of  steam-drams  and  steam-pipes.— Tubular  superheaters  in  uptakes. — Effi- 
ciency and  disadvantages  of  tubular  superheaters  in  uptakes. — Special  superheating  boilers  of 
United  States  naval  vessels.— Superheating  arrangement  of  U.S.S.  Eutaw.—  Its  efficiency  and 
disadvantages. 

CHAPTER  XIV. 

SETTING   AXD   ERECTION  OF  BOILERS. 

Section  1. — Setting  of  Boilers. 

Boiler-kelsons.— Setting  boilers  on  wooden  platforms.— Cements  used  in  setting  boilers.— Care  to  be 
taken  in  setting  boilers.— Saddles  for  dry-bottom  boilers  of  United  States  naval  vessels.— Sup- 
ports for  dry-bottom  boilers' of  U.S.S.  Yantic.— Saddles  for  cylindrical  boilers. 


18  SYNOPTICAL  INDEX. 

Section  2. — Securing  Boilers. 

Section  3. — Erection  of  Sailers  in  the  Vessel. 

Preparing  a  bed  for  the  boilers  and  drawing  the  lines  to  determine  their  position. — Putting  the 
boilers  on  board. — Verifying  their  correct  position. — Securing  them  in  place. — Making  the 
final  connections. — Putting  the  chimney  in  position. 

CHAPTEK  XV. 

BOILER-MOUNTINGS  AND   ATTACHMENTS. 
Section  1. — Grate. 

Usual  form  of  grate. — Dead-plate. — Arrangement  of  grate-bars. — Wrought-iron  grate-bars. — Shape 
and  dimensions  of  grate-bars. — Spaces  between  grate-bars. — Bearing-bars. 

Section  2. — Moving  Orates. 
Various  forms  of  moving  grates. — The  Murphy  shaking-grate. — The  Martin  or  Ashcroft  grate. 

Section  3. — Bridge-walls. 
Forms  of  bridge-walls. — Air-admission  through  bridge-wall. 

Section  4. — Furnace-doors  and  Door-frames. 

Furnace  door-openings. — Furnace  door-frames. — Wrought-iron  furnace-doors. — Cast-iron  furnace- 
doors. — The  Martin  or  Ashcroft  furnace-door. — Pridaux's  furnace-door. — Air-admission 
through  furnace  door. 

Section  5. — Connection-doors,  Ashpit-doors,  and  Ashpans. 

Section  6. — Manhole  and  Handhole  Plates. 

Position,  form,  and  dimensions  of  man  and  handholes. — Strengthening-rings  around  manholes. — 
How  to  determine  the  size  of  strengthening-rings. — Angle-iron  strengthening-rings. — Cast- 
iron  manhole-plates.- — Manhole-plates  for  cylindrical  shells. — Wrought-iron  manhole-cover  by 
Maudslay  Sons  and  Field. — Composition  manhole-covers  for  United  States  naval  boilers. 

Section  7. — Steam  Stop-valves,  Dry-pipes,  and  Steam-pipes. 

General  arrangement  of  steam  stop-valves  on  boilers. — Area  of  steam  stop-valves  and  steam-pipes. 
—Steam  stop-valves  for  boilers  of  U.S.S.  Nipsic. — Dry-pipes. — Steam-pipes. — Arrangement 
of  steam  stop-valves  and  steam-pipes  on  boilers  of  U.  S.  S.  Nipsic. 

Section  8. —  Check-valves  and  Feed-pipes. 

Arrangement  and  form  of  feed  and  check  valves. — Feed  and  check  valves  of  the  boilers  of  U.S.S. 
Nipsic. — Introduction  of  feed- water  into  the  boiler. — Feed-pipes. — Arrangement  of  feed-pipes 
for  boilers  of  U.S.S.  Nipsic. 


SYNOPTICAL  INDEX.  19 

Section  9. — Slow-valves  and  Pipes. 

Brine-pumps. — Blow-valves  of  U.  S.  naval  boilers. — Blow-off  cocks. — Regulation  of  the  Board  of 
Trade  (English)  regarding  blow-off  cocks  and  sea-connections. — Bottom  blow-valves. — Surface 
blow-valve. — Arrangement  of  blow-valves  and  pipes  of  boilers  of  TJ.S.S.  Nipsic. — Material  for 
blow-pipes. 

Section  10. — Instruments  and  Attachments  for  Measuring  and  Indicating  the  Height  and  Density 
of  the  Water,  and  the  Pressure  and  Temperature  of  the  Steam. 

Water-gauges. — Rules  and  Regulations  of  the  Supervising  Inspectors  of  Steam-vessels  regarding 
water-gauges. — Location  and  forms  of  gauge-cocks. — Water-gauge  glasses. — Water-gauges  for 
U.  S.  naval  boilers. — Percussion  water-gauge. — Floats. — Fusible  plugs. 

Salinometer-pots  as  provided  for  TJ.  S.  naval  boilers. — Long's  salinometer-pot — Fithian's  salino- 
meter-pot. 

Steam-gauges. — Thermometers. 

Section  11. — Safety-valves. 

Arrangement  of  safety-valves  on  boilers. — Manner  of  applying  load  to  safety-valves. — Conditions  to 
be  fulfilled  by  a  safety-valve. — Weight  of  steam  discharged  per  second  from  an  orifice. — Effec- 
tive opening  of  safety-valves. — Rules  for  determining  the  area  of  safety-valves. — Various  forms 
of  safety-valves. — Directions  for  the  construction  of  safety-valves  given  by  the  Board  of 
Supervising  Inspectors  of  Steam-vessels.— Safety-valve  for  boilers  of  TJ.S.S.  Nipsic. — Ashcroft 
spring  safety-valve. — Directions  for  the  construction  of  spring  safety-valves  given  by  the  Board 
of  Trade  (England). — Formulae  for  calculating  the  steam  pressure  at  which  a  lever  safety-valve 
will  open,  the  weight  of  the  load  required  for  a  given  length  of  lever,  and  the  length  of  lever 
for  a  given  load. — Practical  method  of  loading  a  lever  safety-valve. 

Section  12. — Miscellaneous  Attachments  of  Boilers. 

Escape-pipes. — Justice's  quieting-chambers. — Shaw's  spiral  nozzles. — Bleeding  valves  and  pipes. — 
Reverse  or  vacuum  valves. — Auxiliary  stop- valves  and  steam-pipes. — Drain-cocks. — Drain-pipes 
in  U.S.S.  Nipsic. 

Section  13. — Covering  for  Boilers. 

General  considerations  concerning  the  covering  of  boilers. — Air-tight  iron  casings. — Cow-hair  felt. 
— Mastic  compositions. — Mineral  wool. 

Section  14. — Feed-water  Heaters  and  Filters. 

Advantages  of,  and  saving  effected  by  heaters.— Feed- water  heater  of  U.S.S.  Waiash. — The  Berry- 
man  heater. — Selden's  filter. 

Section  15. — Feed-pumps  and  Injectors. 

Size  of  feed-pumps. — Simplest  form  of  the  feed- water  injector. — Its  action. — Fixed-nozzle  injector 
and  adjustable  injector.— Lifting  power  of  the  injector. — Quantities  of  steam  and  water  ad- 
mitted.— Formulae. — Duty  of  an  injector. — Experiments  made  on  Irwin's  injector. — Relative 
efficiency  of  injectors  and  pumps. — Use  of  injectors  for  feeding  marine  boilers. — Seller's 
self-adjusting  injector. — Koerting's  universal  lifting  injector. 


20  SYNOPTICAL  INDEX. 

CHAPTER  XVI. 
TESTS,  INSPECTIONS,   AND  TKIALS  OF  STEAM  BOILERS. 

Section  1. — Testing  Boilers. 

Hydraulic  test-pressure. — Section  4418  of  the  U.  S.  Revised  Statutes. — Testing  U.  S.  naval  boilers. 
— Testing  French  boilers. — Regulations  of  Board  of  Trade  (English)  regarding  tests  of  boilers. 
— Anderson  on  testing  boilers. — Manner  of  applying  the  hydraulic  test. — Examination  of  boil- 
ers during  the  test. — Duration  of  tests. — Cold  and  hot  water  tests. — Test  by  expansion  of 
water. — Testing  new  boilers  by  steam. 

Section  2. — Inspection  of  Boilers. 

Necessity  of  careful  inspection. — Section  4418  of  TJ.  S.  Revised  Statutes. — Regulations  of  the  Board 
of  Trade  (English)  for  the  survey  of  marine  boilers. — Particular  points  to  which  the  attention 
of  inspecting  officers  should  be  directed. — Hammer  test. — Drilling  plates. 

Section  3. — Trials  of  Boilers. 

Objects  of  trials. — Boiler  experiments  made  under  the  direction  of  the  Bureau  of  Steam  Engineer- 
ing, U.  S.  Navy  Department. — Rules  to  be  observed  in  making  boiler-experiments. — Duration 
of  experiments. — Reduction  of  results  to  a  uniform  standard  — Extract  from  the  report  on 
the  Murphy  grate,  describing  manner  of  making  experiment. — Extract  from  report  on  the 
Ashcroft  furnace-doors  and  grate-bars,  describing  an  approximate  method  for  determining 
the  temperature  of  the  gases  in  the  uptake. — Methods  for  eliminating  errors  due  to  presence  of 
unvaporized  water  in  the  steam. 

CHAPTER  XVII. 

MANAGEMENT   OF   BOILERS. 

Section  1. — Getting  up  Steam. 

Closing  the  boiler. — Making  the  joint  of  manhole-plates. — Examination  of  valves. — Filling  the 
boiler. — Preparing  the  boiler  for  starting  fires. — Charging  the  furnaces. — Starting  fires. — Time 
required  for  getting  up  steam. 

Section  2. — Firing. 

Thickness  of  the  bed  of  fuel. — Frequency  of  firing. — Back-draught. — Cleaning  fires. — Burning  slack 
and  coal-dust. — Burning  bituminous  coal. 

Section  3. — Management  of  Boilers  under  Steam. 

How  to  obtain  a  uniform  supply  of  steam. — Increasing  the  evaporation. — Using  a  fraction  of  the 
boiler-power. — Banking  fires. — Diminishing  the  steam  supply  temporarily. — Stopping  the  en- 
gines.— Opening  the  safety-valves. — Care  of  water-gauges  — Foaming. — Low  water. — Leaks. — 
Plugging  leaky  tubes. — Putting  a  boiler  out  of  use. — Blowing-down. 


SYNOPTICAL  INDEX.  21 

Section  4. — Foaming:  Its  Cause*,  Effects,  and  Prevention. 

Indications  of  foaming. — Foaming  caused  by  dirty  water. — Foaming  prevented  by  the  use  of  molten 
tallow. — Foaming  due  to  insufficient  and  low  steam-room. — Foaming  due  to  defective  circula- 
tion.— Methods  of  improving  the  circulation. — Increasing  the  steam-room  by  cutting  out 
tubes. — Foaming  caused  by  sudden  reduction  of  pressure. — The  evil  of  foaming  cured  by  the 
use  of  dry-pipes,  steam-drums,  and  superheaters. 

Section  5. — Constituents  of  Saline  Matter  in  Sea-water. 

Density  of  sea  water,  and  proportion  of  salt  in  waters  of  different  seas. — Analysis  of  the  water  of 
the  English  Channel  at  Brighton  by  Dr.  Schweitzer. — Analysis  of  the  water  of  the  Mediterra- 
nean by  Dr.  Laurens. — Carbonate  of  lime. — Sulphate  of  lime. — Chloride  of  calcium. — Chloride 
of  sodium. — Chloride  of  magnesium. — Sulphate  of  magnesia. 

,  Section  6. — Composition  of  Boiler-scale. 

Section  7. — Const? s  Tfieory  of  the  Formation  of  Deposits  in  Steam  Boilers. 
Section  8. — Prevention  of  the  Formation  of  Scale  in  Boilers. 

Section  9. — The  Hydrometer. 

Principle  of  its  action. — Description  of  the  hydrometer  used  in  the  United  States  Navy. — Method 
of  graduating  the  instrument. — The  scale  varies  with  the  temperature. — The  divisions  of  the 
scale  are  not  uniform. — Increase  of  boiling-point. 

Section  10.— Influence  of  Temperature  and  Pressure  on  the  Limit  of  the  Saturation  of  Water  in  a 

Boiler. 

Formation  of  deposits  of  sulphate  of  lime  at  high  temperatures. — Effect  of  blowing-off  under  cer- 
tain conditions. — Table  XXXVIII.,  containing  the  conditions  accompanying  the  saturation 
of  sea-water  with  regard  to  sulphate  of  lime  at  various  pressures  and  temperatures. 

Section  11.— Calculation  of  the  Quantities  of  Water  and  Heat  Lost  by  Blowing-off. 

Section  12. — Cleaning  and  Scaling  Boilers. 

Sweeping  tubes. — Tube-brushes.— Tube-scrapers. — Removing  salt  from,  tubes. — Cleaning  uptakes, 
back-connections,  furnaces,  and  chimneys. — Cleaning  outside  of  boilers. — Painting  boilers. — 
Scaling  boilers.— Washing  out  the  boiler.— Drying  the  boiler. 

Section  13. — Repairing  Boilers. 

Locating  a  leak.— Leaky  seams  and  rivets.— Leaky  stay-bolts.— Patching  a  boiler.— Blisters,— 
Cracks. — Repairing  a  furnace-crown  which  has  come  down. — Leaky  tubes. — Removing  a  tube. 
— Bulged  tube-plate. — Iron  cement  for  leaky  seams  of  old  boilers. — Use  of  oatmeal  for  stop- 
ping leaks.— Filling  the  water-bottoms  with  cement. 


22  SYNOPTICAL  INDEX. 

Section  14. — Preservation  of  Boilers. 

Forming  a  protective  coating  of  scale. — Portland  cement  a  substitute  for  scale. — Coating  the  inte- 
rior of  boilers  with  paint  or  oil. — Systems  used  in  the  English  navy  for  the  preservation  of 
boilers  not  in  use. 

Section  15. — Extract  from  "Instructions  for  the  Care  and  Preservation  of  the  Steam  Machinery 

of  United  States  Naval  Vessels  "  (1879). 


CHAPTER  XVIII. 

CAUSES  AND  PREVENTION  OF  THE   DETERIORATION   OF  BOILERS. 

Section  1. — General  Causes  of  the  Deterioration  of  Boilers. 

Principal  causes  of  deterioration. — Greater  durability  of  stationary  boilers  compared  with  that  of 
marine  boilers. — Speedy  deterioration  of  boilers  of  naval  vessels. — Manner  in  which  deteriora- 
tion takes  place. — Oxidation  of  iron  by  superheated  steam. — Corrosion  of  steel  and  wrought- 
iron. — Corrosion  a!  tacks  surfaces  in  an  irregular  manner. — Pitting. — Grooving. 

Section  2. — Deterioration  caused  by  Overheating  and  by  the  Corrosive  Action  of  the  Gases  of  Com- 
bustion. 

Oxidation  in  furnaces  and  combustion-chambers. — Sulphurous  fuel. — Mechanical  action  of  cinders 
and  fine  coal  in  locomotives.-  Superheating  surfaces. — Overheating  of  plates  when  bared  of 
water. — Blisters. — Spheroidal  condition  of  the  water. 

Section  3. — Strains  produced  by  Sudden  Variations  and  Great  Differences  of  Temperature. 

Intensity  of  stress  produced  by  differences  of  temperature. — Difficulty  experienced  with  steel  boiler- 
plates.— Cracks  in  laps. — Long  furnace-flues. — Difference  of  temperature  in  upper  and  lower 
half  of  furnace-flues  and  of  cylindrical  boiler-shells. — Regulation  of  Board  of  Supervising  In- 
spectors of  Steam-vessels  regarding  temperature  of  feed-water. — Specimens  of  rivets  from  the 
shell  of  a  cylindrical  flue-boiler. — Strains  in  flat  stayed  surfaces  of  shell  and  fire-box  of  loco- 
motive-boilers. 

Section  4. — Formation  of  certain  Saponaceous  Deposits  in  Land  Boilers. 
Extract  from  an  article  by  Maurice  Jourdain.— Comments  of  L.  Delaunay  on  the  foregoing  account. 

Section  5. — Corrosion  of  Steam  Boilers  by  Sulphuric  Acid  present  in  the  Soot. 

Extract  from  an  article  in  the  Annales  des  Mines  et  des  Fonts  et  Chaussees  (1876). — Extract  from 
an  essay  on  "  The  Acid  Products  of  the  Combustion  of  Coal,"  by  M.  Vincotte. 

Section  6. — Corrosion  Due  to  the  Presence  of  Oxygen  and  Carbonic  Acid  in  Water. 

Most  common  cause  of  corrosion,  or  rusting  of  iron. — Pure  distilled  sea-water. — Experiments  made 
by  Scheurer-Kestner  and  Meunier-Dollfus. — Experiments  on  the  oxidation  of  iron  by  Pro- 
fessor P.  Crau-Cal vert. —Extracts  from  Third  Report  of  the  Admiralty  Committee  on  Boilers. 


SYNOPriCAL  INDEX.  23 

Section  7. — Corrosive  Action  of  the  Chloride  of  Magnesium. 

Decomposition  of  chloride  of  magnesium  by  heat. — Experiments  on  the  decomposition  of  chloride 
of  magnesium  by  the  Admiralty  Committee  on  Boilers. — Reactions  between  chloride  of  magne- 
sium and  iron.— Sweating  of  boilers. 

Section  8. — Corrosive  Action  of  Fatty  Acids. 

Decomposition  of  a  fatty  body  in  the  presence  of  certain  calcium  and  magnesium  salts. — Water- 
sapouification. — Professor  A.  W.  Hoffmann  on  the  corrosive  influence  of  water  and  fatty  acids 
upon  iron. — Professor  V.  Wartha  on  the  action  of  fatty  acids  on  iron. — Professor  A.  W.  Hoff- 
mann on  the  action  of  fatty  substances  on  copper. — Corrosive  action  of  fatty  acids  in  steam 
boilers. — Corrosion  of  steam-drums  of  U.S.S.  Swatara. — Means  of  preventing  corrosion  of 
steam  boilers  by  fatty  acids. — Difference  in  the  action  of  tallow  or  vegetable  oils  and  of  mine- 
ral oils  upon  copper. 

Section  9. — Corrosion  of  Boilers  by  Galvanic  Action. 

Galvanic  action  by  contact  of  electro-heterogeneous  metals. — Galvanic  action  of  copper  in  boilers. — 
Galvanic  action  of  lead  in  boilers. — Means  of  preventing  corrosion  of  boilers  by  galvanic  action. 
— Black  magnetic  oxide  of  iron. — Professor  Barff's  method. — Electro-negative  character  of  the 
black  oxide  of  iron. 

Section  10. — The  Use  of  Zinc  for  the  Prevention  of  Corrosion  and  Incrustation  of  Boilers. 

Extract  from  Third  Report  of  the  Admiralty  Committee  on  Boilers  relating  to  the  use  of  zinc  in 
boilers. — Extract  from  an  article  by  Brossard  de  Corbiguy  in  the  Annales  des  Mines  (1877)  re- 
lating to  the  use  of  zinc  for  preventing  the  formation  of  adhesive  scale. — Manner  of  securing 
the  zinc  in  boilers. 

Section  11. — Action  of  Various  Substances  upon  the  Incrustative  and  Corrosive  Ingredients  of  Feed- 
waters. 

Various  processes  of  purification  of  feed-waters. — Difficulties  connected  with  the  chemical  treat- 
ment of  feed-water  for  marine  boilers. — Oil-cakes,  potatoes,  and  other  starchy  matter. — Glue, 
hoofs,  horns,  tobacco-juice,  Irish  moss,  peat,  tow,  hemp. — Clay. — Varnishes  or  lacquers. — Pe- 
troleum or  paraffine  oil. — Glycerine. — Milk  of  lime  and  caustic  lime. — Hetet's  process. — Carbon- 
ate of  soda,  caustic  soda,  and  potash. — Hyposulphite  and  oxalate  of  soda. — Proto-chloride  of 
tin,  silicate,  phosphate  and  arseniate  of  soda. — Chloride  of  ammonium. — Tannic  acid. — Tannate 
of  soda. — Acetic  acid. — Rogers's  process. — Organic  matter,  sewage,  bilge- water. 

CHAPTER  XIX. 

BOILER-EXPLOSIOXS. 

Section  1. — Causes  of  Boiler-explosions. 

Rupture  due  to  weakness  or  to  excessive  pressure. — Causes  of  weakness  in  a  boiler. — Causes  produc- 
ing an  excess  of  pressure. — Circumstances  making  safety-valves  inoperative. — Overheating  of 


24  SYNOPTICAL  INDEX. 

plates. — Violent  shocks. — Detonation  of  inflammable  gases  in  flues. — Explosions  in  consequence 
of  injuries  to  the  shell  of  boilers  and  their  attachments. — Local  damages. — Rupture  producing 
an  explosion. 

Section  2. —  Various  TJieories  concerning  Boiler-explosions. 

Explosions  ascribed  to  obscure  causes. — Electrical  theory. — Detonation  of  hydrogen  and  oxygen 
gases. — Decomposition  of  water  by  heat  alone. — Spheroidal  state  of  water. — Superheating 
water  deprived  of  air. — Superheated  steam. — Overheated  plates. — Forces  generated  in  the  ex- 
plosion of  a  boiler. — R.  H.  Thurston's  calculation  of  the  work  done  in  exploding  a  boiler. 

Section  3. — Phenomena  of  Boiler-explosions. 

Conditions  affecting  the  character  of  an  explosion. — Influence  of  position  of  fracture. — Influence  of 
strength  of  material  in  vicinity  of  original  fracture. — Rupture  of  stays. — Collapse  of  flues  and 
tubes. — Collapse  of  furnace  crowns. — Ruptures  in  cylindrical  and  rectangular  boilers. — Explo- 
sion on  the  Thunderer. — Explosions  of  locomotive-boilers. — Rupture  at  longitudinal  seams  of 
cylindrical  shells. — Explosion  on  the  steamer  Westfield. 

Section  4. — Investigation  of  Boiler-explosions  ( Wilson). 
Section  5. — Experimental  Steam-boiler  Explosions. 

Experiments  at  Sandy  Hook,  N.  J.,  in  1871. — Explosion  of  a  return-flue  boiler. — Explosion  of  an 
experimental  flat  box. — Report  of  Board  of  U.  S.  Naval  Engineers  on  explosion  of  an  old  return- 
tube  boiler. 


LIST  OF  PLATES. 


PLATE  CHAPTER 

I.     Rodman's  Testing-machine  at  Washington  Navy- Yard V. 

II.    Experiments  on  Tensile  Strength  of  Wrought-iron,  conducted  at  the 

Washington  Navy- Yard  by  Chief  Engineer  Win.  H.  Shock,  TT-S.N..  V. 
IIL    Fig.  1.  Boiler  for  U.  S.  S.  Daylight.— fig.  2.  Two  Boilers  for  U.  S.  S. 

Kansas.— Fig.  3.  Two  Boilers  for  F.  S.  S.  Mahaska VII. 

IV.     Boiler  for  Passenger  Locomotive VII. 

V.     Boiler  for  Consolidation  Freight  Locomotive VII. 

VI.     Boiler  for  U.  S.  S.  Lackawanna VII. 

VII.     Boiler  for  U.  S.  S.  Lackawanna VII. 

VEIL     Six  Boilers  for  TJ.  S.  S.  Miantonomoh.  and  Class VII. 

IX.     Bracing  of  Boilers  for  U.  S.  S.  Miantonomoh  and  Class VII. 

X.     Plates  for  Boiler  of  Steamer  Lookout.— Plates  for  Boilers  of  U.  S.  S. 

Nipsic VII. 

XL     Boiler  for  Steamer  Lookout VII. 

XII.     Six  Boilers  for  U.  S.  S.  Nipsic VII. 

XIII.  Details  of  Riveting  of  Boilers  for  U.  S.  S.  Nipsic VII. 

XIV.  Fig.  1  and  2.  Method  of  drilling  Cylindrical  Boilers,  Navy-Yard,  Nor- 

folk, Va.,  18T9 VIII. 

XV.     Two  Boilers  for  S.  S.  Lord  of  the  Isles IX. 

XVI.     Horizontal  Boiler  for  8'  by  8'  Engine,  U.  S.  S.  Cutters IX. 

XVII.     Four  Boilers  for  TJ.  S.  S.  Plymouth IX. 

XVIII.     Bracing  of  Boilers  for  TJ.  S.  S.  Plymouth IX. 

XIX.     Details  of  Boilers  for  U.  S.  S.  Plymouth.— Fig.  I.  Connection  Doors.— 

Fig.  2.  Furnace  and  Ashpit  Doors.— Fig.  3  to  9.  Details  of  Grate.  IX. 


25 


26 


LIST  OP  PLATES. 


PLATE  CHAPTER 

XX.     Experiments  on  shearing  Wronght-iron  Bolts,  conducted  at  the  Wash- 
ington Navy- Yard,  1868,  by  Chief  Engineer  Wm.  H.  Shock,  U.S.N.    X. 
XXI.     Fig.   1.    Marine  Flue-boiler.— Fig.   2.    Boiler  for  U.  S.  S.  Shockokon. 

—Fig.  3.  Boiler  for  U.  S.  S.  Morse XL 

XXII.     Fig.  1  to  5.  Methods  of  securing  Boiler-tubes.— Fig.  6.  Tweddell's  Hy- 
draulic Tube-expander. — Fig.  7.    Selkirk's  Tube-beader XI. 

XXIII.  Experiment  with  Brass  Tubes,  conducted  at  the  Navy- Yard,  Washington, 

D.  C.,  by  Wm.  H.  Shock,  Chief  Engineer,  U.S.N. ,  1877 XL 

XXIV.  Experiment  with  Iron  Tubes,  conducted  at  the  Navy- Yard,  Washing- 

ton, D.  C.,  by  Wm.  H.  Shock,  Chief  Engineer,  U.S.N.,  1877 XL 

XXV.     Attachment  for  Experiments  with  Tubes XL 

XXVI.     Fig.  1.  The  Perkins  Tubular  Boiler.— Fig.  2.  Marine  Boiler  by  T.  and 

F.  Howard XL 

XXVII.     Fig.  1.  The  Herreshoff  Coil  Boiler.— Fig.  2.  The  Belleville  Boiler XL 

XXVIII.     Fig.  1.  Boiler  for  U.  S.  S.  Cutter.— Fig.  2.  The  Davey-Paxman  Boiler. .  XL 

XXIX.     Fig.  1  and  2.  Uptake  and  Furnace-doors  of  Boilers  for  U.  S.  S.  Nipsic.  XIV. 

XXX.     Arrangement  of  Boilers  in  U.  S.  S.  Nipsic XIV. 

XXXI.     Fig.  1  and  5.  Manhole-plates.— Fig.  2,  3,  4.  Boiler-saddles XIV. 

XXXII.     Fig.  1,  2,  3.  Steam  Stop- valves  and  Feed  valve  of  Boilers  for  U.  S.  S. 

Nipsic XV. 

XXXIII.  Water-gauge  of  Boilers  for  U.  S.  S.  Nipsic XV. 

XXXIV.  Fig.  1.  Safety-valve  of  Boilers  for  U.  S.  S.  Nipsic.—  Fig.  2.  Safety-valve 

approved  by  the  Board  of  Supervising  Inspectors  of  Steam-vessels. 

—Fig.  3.  Ashcroft's  Safety-valve XV. 

XXXV.     Fig.  1.  Koerting's  Jet  Apparatus.— Fig.  2.  Sellers'  Self-adjusting  Injec- 
tor.— Fig.  3.   Koerting's  Universal  Lifting  Injector XV. 

XXXVI.     Specimens  of  Rivets  and  Rivet-heads,  from  Boilers  of  Copper-rolling 

Mill,  Navy- Yard,  Washington,  D.  C.,  1879 XVIII. 


LIST  OF  ILLUSTRATIONS  INSERTED  IN  TEXT. 


FIGURES.                                                                                                SUBJECT.  PAGE 

1   and       2.  Forms  of  test-specimens 96 

3   and       4.  Forms  of  test-specimens 97 

5.  Experimental  flue  for  tests  made  at  Washington  Navy- Yard 113 

6.  Experimental  flue  for  tests  made  at  Washington  Navy- Yard 114 

7   and  '    8.  Diagrams  of  strains  on  oblique  braces 118 

9.  Diagram  of  strains  on  circular  arcs 119 

10.  Diagram  of  strains  on  circular  arcs 120 

11     to       14.  Diagrams  of  strains  on  circular  arcs 121 

10a  to     16a.  Forge-tests  of  angle  and  T-irons  for  boilers  of  English  naval  vessels 150 

15.  Front-head  of  boiler  for  U.  S.  S.  Nipsic 158 

16.  Cylindrical  flue  with  inner  and  outer  courses 159 

17     to      19.  Diagrams  for  laying-off  conical  tubes 160 

20     to      22.  Diagrams  for  laying-off  shell  of  cylindrical  boiler 161 

23   and     24.  Diagrams  for  laying-off  cylindrical  shell  of  steam-dome 162 

25    and     26.  Arrangement  of  bending-rolls 164 

27     to      30.  Forms  of  punches 166 

31.  Shape  of  rivet  in  punched  hole 167 

32.  Drifted  rivet-hole 171 

33.  Steam  riveting-machine  of  Providence  Steam-engine  Company,  Providence, 

E,  1 172 

34.  Form  and  dimensions  of  f-inch  rivet 176 

35     to      37.  Forms  of  rivet-points 176 

38.  Countersunk  rivet-hole 177 

39     to       44.  Forms  of  riveted  lap  and  butt  joints 178 

45.  Arrangement  for  determining  friction  in  riveted  joints 179 

46.  Distortion  of  lap-joint 179 

Z! 


28  LIST  OF  ILLUSTRATIONS  INSERTED  IN  TEXT. 

FIGURES.  SUBJECT.  PAGE 

47  to  50.  Distribution  of  stress  in  riveted  joints 181 

51.  Strained  zones  around  punched  holes 182 

52   and     53.  Strains  in  multiple-riveted  joints 183 

54  to  56.  Modes  of  fracture  in  riveted  joints 186 

57.  Excessive  calking  of  lap-joints 188 

58  and  59.  Fractures  of  zigzag-riveted  joints 189 

60.  Distorting  strain  in  countersunk-riveted  joint 191 

61     to      63.  Diagrams  of  fracture  in  multiple-riveted  joints 193 

64.  Diagonal  lap-joint 198 

65.  Oval  rivets 199 

66.  Covering-plate  for  lap-joint 199 

67.  Forked  covering-plate  for  lap-joint 199 

68   and     69.  Plates  with  thickened  edges 199 

70     to       72.  Diagrams  of  experimental  butt-joints 204 

73.  Ordinary  calking-tools -....• 205 

74.  Connery's  calking-tool 205 

75.  Calking-tool  for  butt-joints 206 

76.  Calked  butt-joint 206 

77.  Calked  lap-joint  and  rivet 206 

78.  Bertram's  method  of  welding  boiler-plates 208 

79     to      82.  Forms  of  welded  joints 208 

83   and      84.  Methods  of  welding  flues 208 

85.  Method  of  welding  cylindrical  boiler-shell 209 

86  to  88.  Forms  of  welded  joints 210 

89.  Method  of  welding  front  plates  of  boilers 210 

90  and  91.  Welded  angle-iron  rings 210 

92.  C.  E.  Emery's  connected-arc  marine  boiler 214 

93  and  94.  Circulation  of  water  with  flat  and  arched  furnace-crowns 223 

95.  Furnace  of  marine  boiler  built  by  J.  &  W.  Dudgeon,  England 223 

96.  Furnace  of  boiler  of  U.  S.  tug  Glance 224 

97.  Furnace  of  marine  boiler  built  by  Laird  &  Son,  England 225 

98.  Mud-drum  in  dry-bottom  boiler 226 

99.  Adamson  joint  for  furnace-flues 227 

100.  T-iron  ring  for  furnace-flues 227 

101.  Bowling-hoop  for  furnace-flues 227 

102.  Angle-iron  strengthening-hoop  for  flues 228 

103.  Attachment  of  braces  in  water-legs  of  boilers 236 


LIST  OF  ILLUSTRATIONS  INSERTED  IN  TEXT. 


FIGURE*  SUBJECT.  PAGE 

104   and    105.  Forms  of  branch-braces , 236 

106.  Bracing  rectangular  boilers  of  French  naval  vessels. 237 

107.  Bent  socket-bolt 244 

108     to     111.  Stays  for  narrow  water-spaces 245 

112.  Diagram  of  forked  stay .• 246 

113.  Triangular  stay  for  water-bottom 246 

114.  Brace  for  ends  of  cylindrical  boiler  built  by  R  Napier  &  Co.,  Glasgow 247 

115.  Branch-brace  used  in  French  naval  boilers. 248 

116   and    117.  Triangular  stays  for  attachment  of  braces  to  furnace-crowns 248 

118.  Simple  form  of  branch-brace 249 

119.  Split  pins 249 

120.  Branch-brace  secured  by  nut 249 

121.  Forked  end  of  rod-brace 250 

122.  Flat  brace 250 

123.  Girder-stay 251 

124   and    125.  Stay-plates  for  top  of  back-connection 251 

126   and   127.  Diagrams  showing  proportions  of  eve-bars 254 

128.  Raymond's  recessed  tube-sheet 272 

129.  Expanded  tube-end 273 

130.  Expanding-roller 273 

131.  Beading  tube-end  with  boot- tool 273 

132.  Beading  tube-end  with  round-headed  hammer 273 

133.  Grate-bar 320 

134.  Murphy  shaking-grate 322 

135.  Martin  furnace-door  and  grate 326 

136.  Manhole-plate  and  frame  for  cylindrical  shell 330 

137.  Wrought-iron  manhole-plate  for  boiler  built  by  Mandslay,  Sons  &  Field,  Eng- 

land   330 

138.  Water-gauge-cock 337 

139.  Diagram  of  lever  safety-valve 346 

140.  Practical  method  of  weighting  lever  safety-valve 347 

141.  Top  of  steam-escape  pipe 348 

142    and    143.  Justice's  quieting-chambers 349 

144   and   145.  Shaw's  noise-quieting  nozzles 350 

146.  Fixed-nozzle  injector 355 

147.  Hydrometer 394 

147a.  Manner  of  securing  zinc  slabs  in  boilers 430 


STEAM    BOILEBS: 


THEIR 


DESIGN,  CONSTRUCTION,  AND  MANAGEMENT. 


CHAPTER  I. 

INTRODUCTORY   REMARKS. 

Ix  the  early  days  of  the  steam-engine,  when  the  working  pressure  was  low,  boilers 
were  made  of  various  materials,  many  of  which  were  soon  discarded ;  cast-iron,  and, 
in  particular  instances,  even  granite  and  wood,  were  used. 

Later,  copper  became  a  favorite  material  for  the  construction  of  boilers,  and  it  re- 
mained in  use  in  the  United  States  Navy  up  to  1858.  Its  discontinuance  was  caused  by 
its  greater  first  cost,  greater  weight  in  the  vessel,  and  greater  difficulty  of  keeping  its 
seams  tight,  than  in  the  case  of  plate-iron,  but  principally  the  former.  It  went  out  of 
use  everywhere  long  before  the  employment  of  steam-pressures  too  high  for  its  tensile 
strength  ;  and,  for  a  long  period  before  its  total  disappearance,  it  was  used  in  national 
navies  only,  on  account  of  its  durability,  as  it  exceeded  iron  threefold  in  that  respect. 
The  greater  cheapness  of  plate-iron  superseded  it  at  once  in  merchant-steamers  as  soon 
as  the  manufacture  of  that  material  was  sufficiently  perfected.  A  serious  objection  to 
copper  for  steamers,  independently  of  its  greater  cost,  was  that  boilers  constructed  of 
it  had  a  much  greater  weight  than  plate-iron  boilers  of  the  same  dimensions  and 
strength,  because  of  its  greater  specific  gravity,  and  of  its  greater  cross-sections  of 
metal  required  by  its  less  tensile  strength  to  support  equal  tensile  strains. 

The  difficxilty  in  keeping  the  joints  of  copper  boilers  water-tight  was  an  important 
practical  defect,  and  arose  from  the  fact  that  the  oxide  resulting  from  copper  corrosion 
has  scarcely  any  adhesion  to  the  metal,  so  that  a  leak  once  commenced  continually 
increased  by  the  washing  away  of  the  material  around  it ;  whereas  the  oxide  resulting 
from  the  corrosion  of  iron  boilers  has  so  strong  an  adhesion  to  its  metal,  and  is  so 

31 


32  STEAM  BOILERS.  CHAP.  I. 

bulky  in  proportion  to  its  metallic  constituent,  that  small  leaks  are  soon  stopped  by 
the  very  corrosion  they  produce. 

The  introduction  of  the  compound  engine,  necessitating  high  boiler- pressures  for  the 
development  of  its  best  economy,  at  once  doubled  and  trebled  the  steam-pressures 
previously  employed  with  simple  engines  supplied  with  steam  from  boilers  having 
rectangular  shells,  compelling  thereby  the  abandonment  of  that  form  and  the  substi- 
tution of  cylindrical  shells.  With  steam-pressures  still  increasing,  and  with  the 
necessity  continually  pressing  for  lighter  weights  of  machinery  with  increased  powers 
for  steamers,  the  joints  of  cylindrical  shells  have  been  changed  from  single  to  double 
and  to  treble  riveted  ;  and  the  tendency  now  is  to"  the  substitution  of  steel  as  a  material 
in  place  of  plate-iron,  of  the  welded  joint  with  covering-plates  in  place  of  riveted  joints, 
and  of  boilers  formed  of  tubes  of  small  diameters  variously  arranged. 

The  essential  parts  of  a  steam-boiler  are  : 

1st.    The  ashpit  or  chamber  lying  beneath  the  grate. 

2d.    The  grate  lying  between  and  separating  the  ashpit  from  the  furnace. 

3d.    The  furnace  or  chamber  lying  immediately  above  the  grate. 

4th.  The  flues  or  tubes,  together  with  their  connecting  chambers,  extending  from 
the  furnace  to  the  chimney. 

5th.  The  chimney. 

6th.  The  water-room  enclosing  the  furnace,  tubes,  flues,  and  connecting  chambers. 

7th.  The  steam-room  lying  above  the  water-room. 

From  the  ashpit  air  is  supplied  through  the  grate  to  the  fuel  lying  upon  it,  the  ash 
from  this  fuel  falling  into  the  pit.  The  grate  supports  the  fuel,  which  is  evenly  spread 
over  it  in  such  a  manner  that  the  air  passing  through  its  interstices  may  be  uniformly 
distributed.  The  furnace  contains  the  fuel  whose  constituents  are  burnt  by  combina- 
tion with  the  oxygen  of  the  air  entering  through  the  grate.  The  portion  of  the  furnace 
above  the  fuel  serves  in  part  as  a  combustion-chamber  where  the  uncombined  gases  of 
the  air  and  fuel  may  be  brought  by  mixture  into  contact  while  still  at  a  sufficiently 
high  temperature  for  combustion. 

The  flues,  the  tubes,  and  their  connecting  chambers,  together  with  the  furnace,  con- 
stitute the  heating  surface  by  means  of  which  the  heat  in  the  gaseous  products  of 
combustion  is  transferred  to  the  water  enveloping  those  surfaces.  The  chimney  de- 
livers into  the  atmosphere  the  gases  of  combustion  after  their  heat  has  been  extracted 
to  the  desired  temperature  by  the  heating  surfaces.  It  also  causes  the  "draught"  by 
means  of  which  a  constant  supply  of  new  air  is  furnished  to  the  fuel,  thereby  render- 
ing the  combustion  continuous.  The  water-room  contains  the  water  to  be  vaporized, 


CHAP.  I.  INTRODUCTORY  REMARKS.  33 

and  the  steam-room  contains  the  steam  after  it  has  been  evaporated.  The  first  may  be 
only  of  sufficient  capacity  to  form  barely  an  envelope  to  the  heating  surfaces  ;  but  the 
latter  must  be  at  least  large  enough  to  prevent  the  pressure  of  the  steam  in  it  from 
sensibly  varying  with  the  intermittent  draughts  of  the  steam-cylinder. 

It  is  quite  evident  that  an  ingenious  engineer  could  form  of  the,  elementary  parts  of 
a  boiler  just  enumerated  an  almost  infinite  number  of  combinations  ;  those  which  have 
actually  been  devised  and  executed  are  so  numerous  that  a  large  space  would  be 
required  to  describe  them,  and  their  description  for  the  most  part  would  be  as  useless 
as  tedious.  As  they  can  be  found  extensively  illustrated  in  Patent-Office  reports  and 
in  existing  engineering  literature,  the  present  essay  will  be  restricted  to  a  consideration 
of  only  such  as  have  been  found  by  long  experience  to  meet  the  requirements  of  prac- 
tice, and  chiefly  of  those  best  adapted  for  use  on  board  of  war  and  ocean  merchant 
steamers. 

The  general  conditions  which  determine  the  peculiar  features  of  marine  boilers  are 
the  following :  the  weight  of,  and  the  space  occupied  by,  the  boilers  in  a  vessel  are 
necessarily  limited  ;  economy  in  fuel  is  required  not  only  on  account  of  its  costr  but  on 
account  of  its  weight  and  the  space  occupied  by  it ;  the  height  of  the  chimney  is  limited, 
and  the  location  of  the  boilers  in  the  hold  of  the  vessel  interferes  with  the  draught ;  the 
great  liability  of  marine  boilers  to  the  evil  effects  of  scale  and  corrosion  makes  it  impe- 
rative that  their  interior  should  be  easily  accessible  for  cleaning  and  repairs  ;  the  roll- 
ing and  pitching  of  the  vessel  strains  the  boilers  and  keeps  their  water  in  constant 
motion  ;  special  precautions  have  to  be  taken  to  guard  against  fire  ;  the  boilers  have  to 
remain  in  action  often  for  weeks,  day  and  night,  without  interruption. 

In  a  man-of-war  the  boilers  must  be  placed  as  low  as  possible,  in  order  to  protect 
them  against  the  chances  of  penetration  by  shot ;  the  duty  required  of  them  is  very 
unequal :  they  may  lie  idle  for  years  ;  at  other  times  steam  may  have  to  be  kept  up  in 
them  for  months  continuously  ;  they  will  be  required  to  develop  their  full  power  only 
on  exceptional  occasions  ;  to  be  prepared  for  all  emergencies,  they  must  be  able  to  gen- 
erate steam  rapidly,  and  preserve  their  efficiency  under  greatly  varying  conditions. 


CHAPTER  H. 


COMBUSTION. 

1.  Elementary  Constituents  of  Fuels.— Chemical  combination  is  always  accom- 
panied by  the  development  of  heat,  and  when  the  latter  is  sufficiently  intense  to  pro- 
duce light  the  combination  is  called  combustion,  and  the  combining  substances  are 
called  combustibles. 

The  chief  combustible  constituents  of  fuel  are  carbon  and  hydrogen,  and  their 
chemical  combination  with  the  oxygen  of  the  atmosphere  is  the  source  of  the  heat 
used  in  steam  boilers.  Most  fuel  contains  also  sulphur  and  nitrogen,  whose  combina- 
tion with  oxygen  likewise  produces  heat,  but  the  amount  is  too  insignificant  for  consid- 
eration in  a  treatise  like  this. 

TABLE  I. 


Name. 

Symbol. 

Proportions   of 
elements  by 
weight. 

Chemical 
equiva- 
lent by 
weight. 

Proportions    of 
elements  by 
volume. 

Chemical  Equiva- 
lent by  volume. 

Specific 
Heat 
at 
constant 
pressure. 

Weight  of  a 
cubic  foot   in 
pounds  at  32° 
and  atmos- 
pheric pressure. 

Volume  in  cubic 
feet  of  one 
pound  at  32° 
and  atmos- 
pheric pressure. 

o 

16 

I 

0.218 

O.O8O7 

11.204 

N 

I 

O.24.4 

0.0784 

12.753 

H 

i 

I 

7.4OE; 

o.  00=56 

178.83 

Carbon  

c 

Sulphur  ...              .  . 

s 

Air   

N?7-r-O2t 

o* 

N79-J-O2I 

0.2^8 

0.0807 

12.387 

Water  

H  O 

*•*  1  1    1    *"••<•,} 

H2  -)-Oi6 

18 

1*000 

62.421;  * 

0.016* 

H2     +  O 

2 

to.  j.8o 

0.0502 

IQ.QI'? 

Carbonic  oxide  

CO 

Ci2  +Oi6 

28 

C      +  O 

2 

0.241; 

0.0781 

12.820 

Carbonic  acid    

CO 

Cl2  4-Ol2 

AA 

C      +O2 

2 

O.2I7 

o.  12^4 

8.IOI 

Olefiant  gas  

CH 

CI2+H2 

1A 

C      -f-H2 

2 

o  ^60 

O.O7Q1? 

12.58 

Marsh  gas  

CH 

Ci2+H4 

16 

C      -4-  HA 

2 

O.^O"? 

0.0447 

22.388 

Sulphuretted  hydrogen 

SH 

S-22  -1-  Ha 

2 

Sulphurous  acid  

SO 

S?2  -\-Ql2 

34 
64 

2 

0.1^4. 

0.1814 

15-15i4 

Bisulphuret  of  carbon  . 

S  C 

864  +Cl2 

76 

2 

o.T=;8 

o-2i-?7 

4.679 

Ammonia  

NH 

NIA  4-  H? 

T  7 

2 

*7 

*  The  weight  and  volume  of  water  are  given  for  the  temperature  at  which  it  attains  its  greatest  density— viz.,  39°. I  Fahr. 
t  For  aqueous  vapor  in  the  gaseous  state,  not  saturated  vapor. 

34 


SEC.  3.  COMBUSTION.  35 

"  Substances  combine  chemically  in  certain  proportions  only.  To  each,  substance 
known  in  chemistry  a  certain  number  can  be  assigned,  called  its  '  cTiemical  equivalent,'' 
and  having  these  properties :  I.  That  the  proportions  by  weight  in  which  substances 
combine  chemically  can  all  be  expressed  by  their  chemical  equivalents,  or  by  simple 
multiples  of  their  chemical  equivalents ;  II.  That  the  chemical  equivalent  of  a  com- 
pound is  the  sum  of  the  chemical  equivalents  of  its  constituents."  (Rankine.) 

The  elementary  substances  entering  into  the  composition  of  the  atmospheric  air,  and 
of  the  combustible  portion  of  different  fuels,  are :  oxygen,  nitrogen,  hydrogen,  carbon, 
and  sulphur.  The  preceding  table  contains  the  principal  chemical  and  physical  proper- 
ties of  these  substances  and  of  the  most  important  compounds  formed  by  them,  as 
found  in  different  fuels  and  in  the  products  resulting  from  their  combustion. 

The  chemical  equivalents  are  given  in  round  numbers,  omitting  fractions  too  small 
to  be  of  consequence  in  calculations  connected  with  the  subject  of  the  present  treatise. 

It  must  be  borne  in  mind  that  atmospheric  air  is  not  a  chemical  compound,  but  a 
mechanical  mixture  of  nitrogen  and  oxygen. 

2.  Temperature  of  Ignition. — At  a  temperature  of  about  750°  Fahr.  solid  bodies 
become  luminous,  emitting  a  dull  red  light ;  the  intensity  of  the  light  increases  with 
the  temperature  till  a  dazzling  white  heat  is  attained.     Gases  become  luminous  only 
during  the  process  of  combustion,  forming  what  is  called  flame.     The  flame  of  gases 
has  little  brilliancy,  unless  intensified  by  the  presence  of  small  particles  of  incandescent 
solid  matter.      Combustion  cannot  be  maintained  at  a  temperature  lower  than  800 
degrees. 

3.  Combustion  of  the  Constituents  of  Fuels. — The  action,  during  combustion 
in  the  furnace,  of  the  principal  constituents  of  the  various  kinds  of  fuel  commonly  used 
is  described  by  Rankine  as  follows  :  (I.)  Fixed  or  free  carbon,  which  is  left  in  the  form 
of  charcoal  or  coke  after  the  volatile  ingredients  of  the  fuel  have  passed  off  by  distilla- 
tion.    It  burns  without  flame  ;  when  raised  to  a  state  of  incandescence,  each  equivalent 
by  weight  <  >f  carbon  combines  with  two  equivalents  of  oxygen,  forming  an  invisible  gas 
called  carbonic  acid.     If  the  carbonic  acid  gas  remains  in  contact  with  incandescent 
carbon  it  dissolves  an  additional  equivalent  of  carbon,  forming  with  it  a  compound 
called  carbon  ic  oxi'le.  which  contains  only  one  equivalent  of  oxygen  for  each  equivalent 
of  carbon.     When,  at  a  sufficiently  high  temperature,  the  carbonic  oxide  comes  in  con- 
tact with  oxygen,  it  absorbs  a  sufficient  quantity  to  form  carbonic  acid,  burning  during 
this  process  with  a  blue  flame. 

(II.)  Hydrocarbons,  such  as  olefiant  gas,  pitch,  tar,  naphtha,  etc.,  all  of  which  must 
pass  into  the  gaseous  state  before  being  burned. 


36  STEAM  BOILERS.  CHAP.  U. 

If  mixed,  on  their  first  issuing  from  amongst  the  burning  carbon,  with  a  sufficient 
quantity  of  air,  these  inflammable  gases  are  completely  burned  with  a  transparent  blue 
flame,  producing  carbonic  acid  and  steam.  When  raised  to  a  red  heat,  or  thereabouts, 
before  being  mixed  with  a  sufficient  quantity  of  air  for  perfect  combustion,  they  disen- 
gage carbon  in  fine  powder,  and  pass  to  the  condition  partly  of  marsh  gas,  and  partly 
of  free  hydrogen  ;  and  the  higher  the  temperature  the  greater  is  the  proportion  of  solid 
carbon  thus  disengaged. 

If  the  disengaged  carbon  is  cooled  below  the  temperature  of  ignition  before  coming 
in  contact  with  oxygen,  it  constitutes,  while  floating  in  the  gas,  smoke,  and,  when 
deposited,  soot. 

But  if  the  disengaged  carbon  is  maintained  at  the  temperature  of  ignition,  and  sup- 
plied with  oxygen  sufficient  for  its  combustion,  it  burns  while  floating  in  the  inflam- 
mable gas,  and  forms  red,  yellow,  or  white  flame. 

(III.)  Oxygen  and  hydrogen,  either  actually  forming  water,  or  existing  in  combina- 
tion with  the  other  constituents  in  the  proportions  which  form  water.  The  presence  of 
water,  or  the  constituents  forming  it,  in  fuel  promotes  the  formation  of  smoke  or  of 
the  carbonaceous  flame,  as  the  case  may  be ;  probably  by  mechanically  sweeping  along 
fine  particles  of  carbon. 

The  absorption  of  the  heat  required  for  the  vaporization  of  the  water  contained  in 
the  fuel,  or  produced  by  its  combustion,  may  reduce  the  temperature  of  the  products 
of  combustion  below  the  ignition-point  of  carbon,  but  not  below  the  dissociation-point 
of  the  hydrocarbons  of  great  molecular  condensation. 

(IV.)  Nitrogen,  either  free  or  in  combination  with  other  constituents.  This  sub- 
stance is  nearly  inert,  and  the  bulk  of  it  passes  off  uncombined. 

(V.)  The  sulphur  of  the  sulphurets  of  iron  and  of  copper  contained  in  many  coals 
forms  sulphuric  acid  when  hydrated,  which  corrodes  the  metal  of  the  boiler. 

(VI.)  Other  mineral  compounds  of  various  kinds  form  the  ash  left  after  the  com- 
plete combustion  of  the  fuel ;  and  also  the  clinker,  or  glassy  material  produced  by 
fusion  of  the  ash. 

4.  Total  Heat  of  Combustion. — Carbon  and  hydrogen  are  the  only  constituents 
of  fuel,  the  combustion  of  which  is  of  practical  value  for  the  generation  of  heat  in  the 
steam  boiler.  The  following  table  contains  the  quantities  of  heat  developed  by  the 
combustion  of  one  pound  of  these  elements  and  of  their  compounds,  as  determined  by 
the  careful  experiments  of  Favre  and  Silbermann,  together  with  the  weight  of  oxygen 
necessary  for  their  combustion,  and  likewise  the  weight  of  air  required  to  furnish  this 
amount  of  oxygen. 


Ssc.1 


COMBUSTION. 


37 


The  thermal  unit,  commonly  employed  by  scientists  who  use  British  measures,  is 
the  quantity  of  heat  required  to  raise  the  temperature  of  one  pound  avoirdupois  of  pure 
water  of  39°.  1  one  degree  on  Fahrenheit's  scale,  the  barometer  standing  at  29.922 
inches  of  mercury  at  32°  Fahrenheit,  at  the  level  of  the  sea,  in  latitude  45  degrees. 

TABLE  II. 


Combustible. 

Pounds   of  oxy- 
gen per  Ib.  of 
combustible. 

Pounds  of  air 
per  Ib.  of  com- 
bustible. 

Total  heat  in 
thermal 
units. 

Pounds  of  water 
that  can  be 
evaporated  un- 
der atmospheric 
pressure  from 

212°.     . 

Hydrogen  

8. 

*4  8 

62.0^2 

64  2 

Carbon  (combustion  producing  carbonic  acid).  .  .  . 
Carbon  (combustion  producing  carbonic  oxide)  .  .  . 
Carbonic  oxide  

2.666 
1-333 

O.C7I 

n.6 

5-8 

2  48* 

14,5°° 
4,400 

J..32Q 

15-0 

4-55 
4.48 

Marsh  gas  

4. 

17  4 

2-?,88* 

24  1 

Olefiant  gas  

34? 

14  O 

21.144 

22.1 

The  production  of  3.66  pounds  of  carbonic  acid  gas  by  the  complete  combustion  of 
one  pound  of  carbon  is  accompanied  by  a  development  of  heat  more  than  three  times 
greater  than  the  amount  of  heat  generated  by  the  incomplete  combustion  of  the  same 
weight  of  carbon,  prodiicing  2.33  pounds  of  carbonic  oxide.  When,  however,  these 
2.33  pounds  of  carbonic  oxide  combine  with  a  sufficient  quantity  of  oxygen  to  form  3.66 
pounds  of  carbonic  acid,  10,100  additional  units  of  heat  are  generated,  so  that  the  total 
amount  of  heat  produced  by  this  twofold  process  is  equal  to  the  heat  produced  by  the 
c<  inversion  of  one  pound  of  carbon  into  carbonic  acid. 

The  total  heat  of  combustion  of  a  compound  of  hydrogen  and  carbon  (with  the 
exception  of  marsh  gas)  is  generally  assumed  to  be  nearly  the  sum  of  the  quantities  of 
heat  which  the  hydrogen  and  carbon  contained  in  it  would  produce  separately  by  their 
combustion. 

In  many  such  compounds,  however,  the  quantity  of  heat  is  greater  than  this  sum, 
depending  on  the  degree  of  condensation  of  the  constituents  in  the  molecule.  In  the 
case  of  perfectly  dry  wood,  in  which  oxygen  exists  in  addition  to  carbon  and  hydrogen, 
it  is  only  the  excess  of  the  latter  over  the  oxygen  constituent  in  the  proportion  neces- 
sary to  form  water  which  produces  a  heating  effect ;  but  this  fact  cannot  be  extended 
inferentially  to  other  compounds  of  carbon,  hydrogen,  and  oxygen — such,  for  example, 
as  coal — for  in  their  cases  their  heating  powers  have  been  experimentally  shown  to  even 
exceed  that  of  the  sum  of  their  full  constituents.  The  heating  power  of  any  hydro- 


38  STEAM  BOILERS.  CHAP.  II. 

carbon  can  only  be  known  by  direct  experiment  upon  it,  bnt  a  sufficiently  close 
approximation  for  practice  can  be  made  by  employing  the  old  law  of  Dulong  based 
on  experiments  with  wood.  This  law  is  that,  when  hydrogen  and  oxygen  exist  in  a 
'compound,  only  the  surplus  of  hydrogen,  above  the  amount  required  for  combination 
with  the  oxygen  present  in  the  fuel,  will  be  effective  in  raising  the  total  heat  of  com- 
bustion. 

In  computing  the  total  heat  of  combustion  of  a  compound  it  is  convenient  to  substi- 
tute for  the  hydrogen  a  quantity  of  carbon  which  would  give  the  same  quantity  of 

(62  032  \ 
'       j=4.28. 

On  these  principles  are  based  the  following  general  formulae  for  computing  the  theo- 
retical calorific  power  of  any  compound  of  which  the  principal  constituents  are  carbon, 
hydrogen,  and  oxygen. 

C,  ff,  and  0  represent  the  fractions  of  one  pound  of  the  compound,  which  are, 
respectively,  carbon,  Tiydrogen,  and  oxygen  ;  V  is  the  total  heat  of  combustion  of  the 
compound,  expressed  in  British  thermal  units  ;  and  E  denotes  the  theoretical  vaporific 
power  of  one  pound  of  the  compound,  expressed  in  pounds  of  water  vaporized  from 
212°  under  atmospheric  pressure  ;  then 

U=  14,500     <7+4.28j7-  -          .[I.] 


The  actual  calorific  power  of  coals  cannot  be  determined  with  exactness  by  the 
above  method,  for  the  following  reasons  : 

1st.  Different  forms  of  pure  carbon  differ  considerably  in  calorific  power.  According 
to  Favre  and  Silbermann,  wood  charcoal  has  the  highest  calorific  power,  equal  to  14,544 
units,  and  diamond  has  the  lowest,  equal  to  13,986  units. 

2d.  The  quantity  of  heat  which  becomes  latent  in  the  decomposition  of  the  various 
chemical  compounds  entering  into  the  composition  of  coals  before  combustion  takes 
place,  varies  with  the  nature  of  these  compounds.  The  recent  experiments  of  Scheurer- 
Kestner  and  C.  Meunier  developed  in  many  instances  great  discrepancies  between  the 
actual  and  the  calculated  calorific  powers  of  coals.  In  the  case  of  two  coals,  the  one 
from  Ronchamp  and  the  other  from  Creusot,  which  contained  almost  precisely  the 
same  proportions  of  carbon,  hydrogen,  and  oxygen,  the  calorific  powers,  instead  of 
being,  in  accordance  with  calculation,  identical,  were  16,411  and  17,320  respectively. 
The  difference  between  the  real  and  calculated  calorific  powers  amounted  in  some 
instances  to  as  much  as  15  per  cent. 


SEC.  5,  COMBUSTION.  39 

The  quantity  of  heat  that  may  be  generated  by  the  complete  combustion  of  a  fuel 
is  not  the  measure  of  its  vaporific  power  in  a  steam  boiler ;  the  latter  depends  in  a  great 
measure  on  the  temperature  of  combustion,  and  the  completeness  of  the  combustion  of 
the  fuel  in  the  boiler,  and  can  be  determined  only  by  experiment  under  conditions  of 
actual  practice  (see  Tables  V.,  VI.,  and  VI.  a).  The  utilization  of  the  large  quantity 
of  heat  generated  by  the  combustion  of  hydrogen  presents  great  practical  difficulties, 
and  Johnson's  experiments  on  the  vaporific  power  of  American  and  English  coals,  made 
in  1842-43,  established  the  fact  that,  when  the  weight  of  fixed  carbon  is  less  than  four 
times  the  weight  of  the  volatile  combustible  matter  in  a  coal,  its  vaporific  power  in  a 
steam  boiler  decreases  perceptibly. 

5.  Fuel  as  a  Source  of  Power. — By  multiplying  the  units  of  heat  representing 
the  calorific  power  of  a  fuel  by  "Joule's  equivalent"  we  find  the  amount  of  energy 
stored  up  in  the  fuel  and  set  free  by  its  combustion. 

Dr.  Joule,  of  Manchester,  found,  by  carefully-conducted  experiments,  the  result  of 
which  he  finally  communicated  to  the  Royal  Society  in  1849,  that  each  British  unit  of 
heat  was  produced  by  the  expenditure  of  772.69  foot-pounds  of  work.  Other  observers 
who  have  since  tried  to  determine  the  mechanical  equivalent  of  heat  by  various  meth- 
ods have  obtained  results  differing  more  or  less  from  that  of  Joule's  experiments.  The 
mean  of  sixteen  of  the  most  accurate  of  these  determinations  gives  786  as  the  value  of 
the  mechanical  equivalent  of  heat.  At  a  meeting  of  the  Royal  Society,  held  January 
24,  1878,  Joule  read  a  paper  in  which  he  gives  an  account  of  the  experiments  he  had 
recently  made,  with  a  view  to  increase  the  accuracy  of  the  results  given  in  his  former 
paper.  The  result  he  has  now  arrived  at  from  the  thermal  effects  of  the  friction  of 
water  is  that,  taking  the  unit  of  heat  as  that  wjiich  can  raise  a  pound  of  water,  weighed 
in  vacuo,  from  60°  to  61°  Fahr.  of  the  mercurial  thermometer,  its  mechanical  equivalent 
reduced  to  the  sea-level,  at  the  latitude  of  Greenwich,  is  772.55  foot-pounds. 

For  calculations  the  value  of  "Joule's  equivalent''1  is  generally  taken  as  772,  in 
round  numbers. 

A  recent  and  careful  determination  of  the  mechanical  equivalent  of  heat  was  made 
by  a  Commission  of  the  French  Academy,  which  found  that  789J  foot-pounds  of  work 
were  equivalent  to  the  heat  required  to  raise  the  temperature  of  one  pound  of  water  at 
32°  to  33°  under  the  standard  atmospheric  pressure.  Joule's  determination,  however, 
is  still  generally  employed  in  scientific  works. 

Taking  14.000  units  of  heat  as  representing  the  average  calorific  power  of  good  coal, 
we  find  that  the  energy  developed  by  the  combustion  of  one  pound  of  such  coal  is  equal 
to  14,000  x  772,  or  10.808,000  foot-pounds. 


40  STEAM  BOILERS.  CHAP.  H. 

6.  Air  required  for  Combustion. — To  ensure  the  perfect  combustion  of  a  fuel 
it  is  necessary — 

First,  to  maintain  the  combustible  matter  at  such  a  temperature  as  is  required  for 
its  chemical  combination  with  the  oxygen  of  the  air. 

Secondly,  the  quantity  of  air  admitted  to  the  furnace  must  contain  a  sufficient 
amount  of  oxygen.  If  C,  H,  and  0  represent  the  same  quantities  as  in  equation  [I.], 
and  A  represents  the  number  of  pounds  of  air  containing  the  quantity  of  oxygen 
required  for  the  complete  combustion  of  one  pound  of  combustible,  then 

A  =  11.6  (7+34.8  ill-  ~Y[IIL] 

For  all  practical  purposes  it  is  sufficiently  accurate  to  assume  the  quantity  of  air  chemi- 
cally required  for  every  kind  of  coal  as  12  pounds  per  pound  of  coal. 

Thirdly,  the  air  must  be  thoroughly  mixed  and  brought  into  actual  contact  with 
each  particle  of  the  incandescent  solid  and  gaseous  matter.  In  the  furnace  of  a  steam 
boiler  this  is  effected  in  two  ways,  viz. :  First,  by  admitting  the  air  partly  below  the 
fuel,  through  the  evenly-distributed  interstices  of  the  grate,  and  partly,  in  the  shape 
of  numerous  small  jets,  above  the  solid  fuel  among  the  evolved  gases  in  the  furnace ; 
and,  secondly,  by  admitting  a  quantity  of  air  in  excess  of  the  theoretical  quantity 
required  by  formula  [III].  The  amount  of  this  excess  varies  with  different  coals  and 
with  the  manner  of  introducing  the  air ;  but  numeroiis  experiments  have  proved  that 
in  ordinary  boiler-furnaces,  where  the  draught  is  produced  by  means  of  a  chimney, 
the  total  weight  of  air  admitted  should  be,  on  an  average,  twice  the  amount  theoreti- 
cally required  for  the  oxidation  of  the  fuel,  or  24  pounds  per  pound  of  coal  burned ; 
when,  however,  the  draught  is  produced  by  artificial  means,  either  by  a  steam- jet  or  by 
a  fan-blower,  one  and  a  half  times  the  theoretical  amoiint,  or  18  pounds  per  pound  of 
coal,  appear  to  be  sufficient. 

While  an  admission  of  air  in  excess  of  the  amount  actually  required  for  the  com- 
plete oxidation  of  the  fuel  always  entails  a  loss  of  heat,  since  the  temperature  of  the 
uncombined  air  has  to  be  raised  at  the  expense  of  the  heat  of  combustion,  the  loss  of 
heat  in  consequence  of  incomplete  combustion  is  generally  far  greater. 

7.  Temperature  of  Combustion. — The  elevation  of  the  temperature  of  the  pro- 
ducts of  combustion,  above  the  temperature  at  which  the  air  and  the  fuel  are  supplied 
to  the  furnace,  which  would  be  obtained  if  the  combustion  was  complete,  and  the  whole 
heat  of  combustion  was  spent  in  raising  the  temperature  of  the  products  of  combustion, 
is  called  the  theoretical  calorific  intensity  of  the  fuel,  and  is  computed  by  dividing  the 
total  heat  of  combustion  of  one  pound  of  fuel  by  the  sum  of  the  products  of  the  weight 


SEC.  7. 


COMBUSTION. 


and  specific  heat  of  the  several  products  of  combustion,  under  constant  pressure. 
When  steam  is  present  among  the  products  of  combustion,  resulting  either  from  the 
combustion  of  hydrogen  or  from  water  mechanically  combined  with  the  fuel,  the  pro- 
duct of  its  weight  and  latent  heat  must  be  deducted  from  the  total  heat  of  combustion 
in  the  first  place.  The  specific  heat  of  varioiis  products  of  combustion  has  been  given 
in  Table  I.;  that  of  ashes  is  probably  about  0.200. 

The  latent  heat  of  steam  at  ordinary  atmospheric  pressure  is  966°.  1. 

TABLE  III. 

CONTAINING  THE  THEORETICAL  TEMPERATURES  PRODUCED  BY  THE  PERFECT  COMBUSTION  OF 

VARIOUS  SUBSTANCES. 


Name  of  substance. 

Pure  oxygen  supplied 
sufficient  for 
complete  combustion. 

Atmospheric  air  supplied. 

Sufficient  for 
complete  oxidation. 

One  and  a  half  times 
the  quantity  necessary 
for  complete  oxidation  . 

Twice  the  quantity 
necessary  for 
complete  oxidation. 

Hydrogen  

I2,3460 

18,257° 
12,695° 

15,475° 

4,9"° 
4,866° 

5,358: 
4-897° 

3,556° 

33*6 
3.921 
3,420 

2.787° 
2,526° 

3,094° 
2,627° 

Carbon  

Carbonic  oxide  

Olefiant  gas  

Experiments  on  the  combustion  of  hydrogen  and  carbonic  oxide  by  Bunsen  indicate 
that  the  temperature  of  combustion  cannot  exceed  a  certain  limit,  owing  to  the  pheno- 
menon of  "dissociation"  —that  is  to  say,  when  the  temperature  of  combustion  reaches 
this  limit  the  elementary  bodies  no  longer  combine.  When,  for  instance,  hydrogen  is 
burnt  in  presence  of  the  exact  quantity  of  oxygen  necessary  for  complete  combustion, 
the  heat  produced  by  the  combustion  of  a  part  of  the  hydrogen  is  sufficient  to  raise  the 
temperature  of  the  mixture  to  such  an  extent  that  no  further  union  of  the  elements  can 
take  place.  As  soon  as  the  temperature  begins  to  fall  fresh  quantities  of  hydrogen  are 
burnt,  and  this  process  continues  until  the  whole  is  consumed. 

Under  the  conditions  obtaining  in  the  furnace  of  a  steam  boiler  the  temperature  of 
the  products  of  combustion  are  necessarily  always  much  lower  than  the  preceding  table 
indicates,  owing  to  the  more  or  less  incomplete  oxidation  of  the  gases,  the  presence  of 
incombustible  matter  and  of  moisture  in  the  fuel  and  in  the  air,  and  the  cooling  by  ra- 
diation and  conduction.  Ledieu  states  that,  under  conditions  of  ordinary  practice,  the 
temperature  of  the  gases  in  the  furnace  of  a  marine  boiler  will  hardly  exceed  1500°, 
with  a  combustion  of  about  19  pounds  of  semi-bituminous  coal  per  square  foot  of  grate 
per  hour. 


STEAM  BOILERS. 


CHAP.  1L 


8.  Volume  of  Products  of  Combustion. — An  inspection  of  Table  I.  will  show 
that,  at  equal  temperatures,  the  volume  of  carbonic  acid  gas  is  the  same  as  that  of  the 
oxygen  entering  into  its  composition  ;  but  that  the  volume  of  steam  is  double  the  vol- 
ume of  oxygen  required  for  the  combustion  of  the  hydrogen  entering  into  its  composi- 
tion. Since,  in  the  coals  used  in  marine  boilers,  hydrogen  bears  only  a  small  proportion 
to  the  whole  weight,  the  volume  of  the  gaseous  products  of  combustion  may  be  treated 
as  practically  equal  to  that  of  the  air  supplied  to  the  furnace.  The  volume  of  air  at  32° 
may  be  taken,  in  round  numbers,  as  12^  cubic  feet  for  each  pound  of  air.  Neglecting 
the  variations  in  density  due  to  the  slight  deviations  of  the  pressure  of  the  furnace- 
gases  from  the  mean  atmospheric  pressure,  as  of  trifling  importance  in  calculations  for 
practical  purposes,  the  volume  of  the  furnace-gases  at  any  temperature  may  be  calcu- 
lated by  the  formula : 

y        T4-  461°  2 
_  A  __L   FTV  i 

F0  '        493°.2 

which  expresses  the  general  law  "  that  the  volumes  of  gases  vary  directly  as  their  ab- 
solute temperatures."  V  and  F0  represent  the  volume  of  the  gas  in  question  at  the 
temperatures  T°  and  32°  respectively. 

The  following  table,  given  by  Rankine,  is  based  on  the  foregoing  assumptions  : 

TABLE  IV. 


Volume  of  gases  in  cubic  feet,  per  pound  of  fuel. 

Supply  of  air, 

Temperature  in 

degrees   Fahrenheit. 

12  pounds 
per  pound  of  fuel. 

18  pounds 
per  pound  of  fuel. 

24  pounds 
per  pound  of  fuel. 

2500 

906 

1359 

1812 

l832 

697 

1046 

1395 

1472 

588 

882 

1  176 

III2 

479 

718 

957 

752 

369 

553 

738 

572 

3i4 

47i 

628 

392 

259 

389 

5i9 

212 

205 

3°7 

409 

104 

172 

258 

344 

68 

161 

241 

322 

32 

J5° 

225 

300 

j 

9.  Rate  of  Combustion. — The  rate  of  combiistion  in  a  furnace  is  measured  by  the 
number  of  pounds  of  fuel  burned  on  a  square  foot  of  grate  per  hour.  The  weight  of 
fuel  which  can  be  burned  depends  on  the  quantity  of  air  which  can  be  made  to  pass 
through  the  furnace  and  part  with  its  oxygen  to  the  combustible  matter.  In  practice, 


SBC.  10.  COMBUSTION.  43 

with  natural  chimney  dranght,  the  rates  of  combnstion  vary  from  7  to  16  pounds  for  an- 
thracite coals,  and  from  12  to  27  pounds  for  bituminous  coals,  in  different  types  of 
marine  boilers.  With  artificial  draught,  produced  by  a  steam-blast  or  fan-blowers,  the 
rate  of  combustion  may  be  raised  to  120  pounds  of  coke  in  certain  types  of  boilers. 

The  high  rate  of  combustion  which  can  be  attained  with  bituminous  coals  is  owing 
to  the  fact  that  these  coals,  on  being  heated  in  the  furnace,  part  readily  with  their 
hydrocarbons  in  the  form  of  gas,  the  solid  portion  of  the  coal  being  either  left  behind 
as  a  .spongy,  porous  mass  (coke),  or  showing  numerous  cracks  all  over  the  surfaces 
which  divide  the  lump  into  a  great  number  of  loosely  cohering  particles.  In  this  man- 
ner the  air  gets  access  to  the  interior  of  the  solid  coal  and  comes  in  contact  with  a  larger 
surface.  The  hard  anthracite  coals,  on  the  contrary,  remain  solid  during  combustion, 
and  the  air  comes  in  contact  only  with  their  exterior. 

1O.  Draught  of  Furnaces.  —  The  velocity  with  which  air  passes  through  the  grate 
of  a  furnace  depends  on  the  difference  of  pressures  existing  within  the  furnace  and  the 
ashpit,  and  on  the  resistance  offered  by  the  layer  of  fuel  on  the  grate.  The  pressure 
below  the  grate  is  the  atmospheric  pressure,  unless  it  is  either  increased  by  forcing  air 
into  the  ashpit  by  means  of  a  fan-blower,  or  diminished  by  preventing  the  free  flow  of 
air  into  the  ashpit.  The  pressure  above  the  grate  in  the  furnace  is  equal  to  the  atmos- 
pheric pressure,  less  the  difference  in  weight  of  a  vertical  column  of  atmospheric  air 
having  a  base  of  a  unit  of  area  and  a  height  equal  to  that  of  the  chimney  and  of  an 
equal  column  of  hot  chimney  -gas,  plus  the  pressure  required  to  overcome  the  various 
resistances  experienced  by  the  gases  in  their  passage  from  the  furnace  up  the  chimney. 
When  by  the  action  of  a  jet  or  fan  the  weight  of  the  column  of  chimney-gas  is  partly 
counterbalanced,  the  pressure  in  the  furnace  is  correspondingly  diminished. 

Peclet  expresses  all  the  resistances  encountered  by  the  gases  in  their  passage  from 
the  ashpit  to  the  top  of  the  chimney  in  terms  of  the  head  corresponding  to  the  velocity 
of  the  air  flowing  to  the  grate,  per  se. 

Calling  this  head  #, 

the  resistance  due  to  the  grate  and  the  bed  of  fuel  GJi, 
the  resistance  due  to  changes  in  sectional  area  and  direction  of  the  flues  C7i, 
and  the  coefficient  of  friction  of  the  gases  moving  over  the  surfaces  of  the  flues/1, 
he  gets  an  expression  of  the  following  form  for  the  total  head  ff,  which  produces  the 
draught  of  a  boiler,  viz.  : 


1  +  0 


where  v  is  the  velocity  of  the  air  flowing  to  the  grate  in  feet  per  second. 


44  .        STEAM  BOILERS.  CHAP.  II. 

•0"    fl/t  V 

In  the  expression  -~-  ^—  \-r-j  ,  which  represents  the  resistance  due  to  friction, 

I  is  the  combined  length  of  the  flues  and  of  the  chimney  in  feet ; 

m  is  the  "hydraulic  mean  depth"  of  the  flues  and  chimney — that  is  to  say,  the  mean 
of  the  area  of  the  smoke-passages  divided  by  their  perimeter  ; 

£,  and  t  are  the  absolute  temperatures  of  the  chimney -gas  and  of  the  external  air  respec- 
tively, and  ~  represents  the  increase  of  volume,  and  consequently  of  velocity, 
ii 

due  to. the  increase  of  temperature  of  the  gases  in  the  flues  and  chimney  over  that 

of  the  entering  air  ; 
f,  the  coefficient  of  friction,  has,  according  to  Peclet,  the  value  0.012  for  currents  of 

gas  moving  over  sooty  surfaces. 

The  value  of  CTi  varies  according  to  the  arrangement,  form,  and  proportions  of  the 
smoke-passages,  and  consists  of  the  sum  of  the  following  resistances,  which  have  to  be 
calculated  according  to  the  laws  governing  the  flow  of  fluids  : 

1. — On  entering  the  tubes  or  flues  the  gases  experience  a  loss  of  head  due  to  the  "con- 
tracted vein." 

2. — Sudden  enlargements  of  the  sectional  area  of  the  passages  produce  a  loss  of  head. 
3. — Each  change  in  the  direction  of  a  current  produces  a  loss  of  head ;    this  loss 
increases  with  the  angle  which  the  two  directions  make  with  each  other,  and  is  far 
greater  for  sudden  sharp  bends  than  for  bends  with  easy  curves. 

4. — Several  currents  entering  a  common  channel,  and  moving  either  with  different  velo- 
cities or  in  different  directions,  produce  a  loss  of  head. 

The  value  of  G  varies  with  the  kind  of  fuel,  the  thickness  of  the  bed  of  fuel  on  the 
grate,  and  the  velocity  of  the  air  passing  through  the  grate.  Peclet  estimates  that 
when  bituminous  coal  is  burnt  at  the  rate  of  about  22  pounds  per  square  foot  of  grate 
per  hour,  the  resistance  of  the  grate  is  8  h,  and  that  this  resistance  varies  as  the  square 
of  the  number  of  pounds  of  coal  burnt  per  square  foot  of  grate  per  hour.  Coke  offers 
much  less  resistance  than  coal. 

In  coke-burning  locomotives  Peclet  found  the  value  of  G-  to  vary  from  5.20  to  6.26, 
and  he  gives  7.14  7i  as  the  mean  value  of  H^  in  locomotives,  viz.:  1.93  Ji  for  the  resist- 
ance of  the  tubes,  and  5.21  7i  for  the  resistance  of  the  grate.  He  remarks,  however, 
that  these  figures  are  merely  rough  approximations  which  may  serve  to  give  an  idea  of 
the  relative  value  of  the  different  kinds  of  resistance. 

In  marine  boilers  located  in  the  holds  of  vessels  there  is  an  additional  loss  of  head, 
due  to  the  work  expended  in  drawing  the  air  through  the  narrow  openings  in  the  deck 


SBC  11.  COMBUSTION.  45 

to  the  ashpits.  Isherwood  states  that,  owing  to  this  cause,  the  rate  of  combustion  of 
horizontal,  return  fire-tube  boilers  falls  from  24  pounds  of  anthracite  consumed  when 
the  boiler  stands  in  an  open  shed,  to  16  pounds  of  anthracite  when  the  boiler  stands  in 
the  hold  of  a  vessel,  natural  chimney-draught  being  used  ;  and  with  the  vertical  water- 
tube  boiler  of  the  Martin  type  the  rate  of  combustion  falls,  under  like  conditions,  from 
16  pounds  to  12£  pounds  of  anthracite  coal. 

11.  Chimney-draught  —  "The  head  produced  by  the  draught  of  a  chimney  is 
equivalent  to  the  excess  of  the  weight  of  a  vertical  column  of  cool  air  outside  the  chim- 
ney, and  of  the  same  height,  above  that  of  a  vertical  column,  of  equal  base,  of  the  hot 
gas  within  the  chimney."  (RanJcine.) 

The  weight  in  pounds  of  a  cubic  foot  of  air  at  atmospheric  pressure  at  any  tempera- 

ture is  given  by  the  formula  :  -  ^  x  0.0807  [VI.], 

t 

where  t  is  the  absolute  temperature  of  the  air. 

The  weight  in  pounds  of  a  cubic  foot  of  the  gas  discharged  by  the  chimney  is  very 
nearly  ^  ^  (m7  +  ^  [yn  ^ 

and  varies  ordinarily  from  0.084  x  493'2  to  0.087  X  —  —  . 

t,  tl 

In  this  formula  V,  is  the  volume  at  32°  of  the  air  supplied  to  the  furnace  per  pound 
of  fuel  ; 
t,  is  the  absolute  temperature  of  the  gas  within  the  chimney. 

If  H  denotes  the  height  of  the  chimney,  the  unbalanced  pressure  producing  the  flow 
of  air  to  the  grate  is  equal  to 

ff**®2  (0.0807)  -  ff^2  Co.  0807  +  -T\  )  : 


or  in  case  300  cubic  feet  of  air  are  supplied  for  each  pound  of  fuel  burned, 

H  ^-2(0.  0807)  -H*®^-  (0.084),    [VIII.] 
39.80124       4 


The  head,  expressed  in  feet  of  the  external  air,  corresponding  to  this  pressure  is 
found  by  dividing  the  foregoing  expression  by  the  weight  of  a  cubic  foot  of  air  : 


(0.0807) 


\ 

=//  (l-  L0409  f);  [IX.] 

I 

/ 


46  STEAM  BOILERS.  CHAP.  II. 

Substituting  this  value  of  If,  in  equation  [V.],  we  get  the  following  expression  for  the 
velocity  with  which  the  air  flows  to  the  grate  of  a  furnace : 


1-1.0409-?-  ~"1 


[X.] 


The  following  conclusions  may  be  drawn  from  this  equation,  viz.:  Under  otherwise 
equal  conditions,  the  velocity  of  the  air  flowing  to  the  grate,  and,  consequently,  the 
rate  of  combustion,  varies  very  nearly  as  the  square  root  of  the  height  of  the  chimney  ; 
strictly  speaking,  it  is  slightly  less,  because  the  value  of  I  in  the  denominator  increases 
likewise  with  the  height  of  the  chimney. 

With  a  fixed  value  of  t,  or  absolute  temperature  of  the  external  air,  the  value  of  the 

numerator,  y  \  — 1.0409  -r ,  increases  with  the  temperature  of  the  chimney,  and  becomes 

v  j 

equal  to  unity  when  t,  is  infinite  ;  but  this  increase  is  very  slow  with  high  temperatures. 
Forexample,  the  temperature  of  the  external  air  being  50°  Fahr.,  the  expression 


V 


1  —  1.0409  -  becomes  equal  to 
* 


.5486,  -        -  .7059,  -  .7804,  -  1.000, 
when  the  temperature  of  the  chimney-gas,  in  degrees  Fahr.,  is 

300°  600°  900°  infinity. 

f  7  If  \3 
Since  the  resistance  due  to  friction,  represented  by  the  expression  J—  l^\  in  the  de- 

f 


nominator,  increases  as  the  square  of  the  absolute  temperature  -of  the  hot  gases,  there 
must  be  a  certain  chimney-temperature  for  which  the  value  of  v  becomes  a  maximiim  ; 
but  this  temperature  varies  with  the  resistances  represented  by  G  and  C  and  with  the 


factor   —  . 
m 

The  value  of  v  is  further  diminished  by  the  cooling  of  the  chimney  -gases  by  the  ra- 
diation and  conduction  of  heat  from  the  smoke-pipe.  This  loss  increases  likewise  with 
the  height  of  the  chimney  and  the  temperature  of  the  escaping  gases. 

Data  are  wanting  to  assign  exact  values  to  the  various  resistances  under  different 
conditions,  but  equation  [X.]  may  be  used  to  find  the  limit  of  the  influence  which  a 
change  of  conditions  can  have  on  the  efficiency  of  a  boiler. 


SBC.  12.  COMBUSTION.  47 

The  height  of  the  chimneys  of  marine  boilers  is  limited  by  practical  considerations, 
and  it  seldom  exceeds  65  feet. 

The  expenditure  of  heat  to  produce  an  increase  in  the  rate  of  combustion  augments 
so  rapidly  after  a  certain  limit  has  been  reached  that  it  is  not  advantageous  to  increase 
the  chimney-temperature  to  the  point  at  which  the  rate  of  combustion  becomes  a  maxi- 
mum. It  is  generally  assumed  that  the  chimney-temperature  of  marine  boilers  should 
not  exceed  600°  Fahr. 

12.  Artificial  Draught. — "The  head  produced  by  a  blast-pipe  is  equivalent  to 
that  part  of  the  atmospheric  pressure  which  is  balanced  by  means  of  the  impact  of  the 
jet  of  steam  against  the  column  of  gas  in  the  chimney." 

"  The  work  which  a  fan  or  other  blowing-machine  must  perform  in  a  given  time  in 
blowing  aii-  into  a  furnace  so  as  to  produce  a  given  head,  is  found  by  multiplying  the 

pressure  equivalent  to  that  head,  in  pounds  on  the  square  foot     H^ — ^—  (0.0807)    into 

the  number  of  cubic  feet  of  air  blown  in,  taken  at  the  temperature  at  which  it  quits 
the  blowing-machine." 

If  tt  is  the  temperature  on  the  absolute  scale  at  which  the  air  leaves  the  blowing- 
machine,  the  net  or  useful  effect  of  the  machine  per  second  will  be 

WF^  5;  (0.0807)      [XI.]; 

when  w  denotes  the  weight  of  fuel  burned  in  the  furnace  per  second, 
and  F0  the  volume  at  32°  of  the  air  supplied  per  pound  of  fuel. 

"The  gross  power  or  energy  required  to  drive  a  blowing-fan  is  greater  than  the  use- 
ful work  in  a  proportion  which  varies  much  in  different  machines  and  is  very  uncer- 
tain." (RanJcine.) 

13.  Efficiency  of  Furnace.— Under  otherwise  equal  conditions  the  rate  of  com- 
bustion varies  very  nearly  as  the  square  root  of  the  height  of  the  chimney. 

This  is  true  on  the  supposition  that  the  mean  temperatures  of  the  chimney -gases 
are  the  same  from  base  to  top  for  the  chimneys  of  different  heights,  and  that  the  gases 
receive  no  frictional  resistance  from  the  sides  of  the  chimney,  neither  of  which  is  prac- 
tically the  case.  In  practice,  when  gases  of  the  same  temperature  enter  the  base  of 
chimneys  of  different  heights  the  temperature  at  the  top  is  different,  owing  to  external 
refrigeration,  etc.,  being  less  as  the  chimney  is  higher,  so  that  the  mean  temperature  in 
the  higher  chimney  will  be  less  than  in  the  lower  one  ;  and  the  velocity  of  the  draught 
of  the  higher  chimney  will  be  less  comparably  with  the  velocity  of  the  draught  of  the 
lower  chimney  than  it  should  be  according  to  the  law  of  the  square  roots  of  the  heights. 


48  STEAM  BOILERS.  CHAP.  II. 

Again,  as  the  Motional  resistances  of  the  sides  of  the  chimney  are  as  the  square  of  the 
velocity  of  the  gases,  the  velocity  in  a  chimney  sufficiently  high  would  become  uni- 
form, after  which  no  fiirther  increase  of  height  would  increase  the  draught. 

An  increase  of  the  furnace-temperature  of  a  boiler  of  given  proportions  causes  an 
increase  of  the  chimney-temperature,  and,  consequently,  of  the  draught ;  and,  vice 
versa,  a  diminution  of  the  furnace-temperature,  in  consequence  of  an  excessive  amount 
of  air  admitted  to  the  furnace  or  of  incomplete  combustion,  causes  a  decrease  of  the 
chimney-temperature  and  of  the  rate  of  combustion. 

In  a  boiler  of  given  proportions  and  dimensions  the  rate  of  combustion  may  be 
varied  by  aiding  the  chimney-draught  by  a  jet  or  fan-blower,  or  by  impeding  it  by 
means  of  a  damper  in  the  chimney  or  flues  ;  by  regulating  the  flow  of  air  to  the  grate 
by  means  of  the  ashpit-doors  ;  or  by  increasing  or  decreasing  the  resistance  of  the  grate 
by  varying  the  depth  of  the  bed  of  fuel. 

The  draught  can  be  regulated  much  more  readily  by  means  of  dampers  placed  in  the 
flues  or  chimney  than  by  closing  the  ashpit-doors. 

When  the  damper  is  closed  the  furnace  is  kept  filled  with  the  gases  of  combustion, 
which,  by  enveloping  the  fuel,  effectually  prevent  its  combustion,  notwithstanding  their 
leakage  out  past  the  damper  accompanied  by  a  corresponding  entrance  of  air,  for  com- 
bustion will  not  take  place  with  the  atmospheric  oxygen  diluted  beyond  a  certain  point. 
But  when  the  ashpit-door  is  closed — the  damper  being  open  or  absent — there  is  a  free 
escape  for  the  gases  of  combustion,  and  all  the  atmospheric  oxygen  leaked  in  is  available 
for  combustion.  Were  damper  and  ashpit-door  perfectly  tight  both  would  be  equally 
efficacious. 

The  thickness  of  the  bed  of  fuel  can  be  varied  only  between  certain  limits  ;  for,  when 
the  bed  is  too  thin,  too  large  a  quantity  of  air  will  rush  through  the  grate  ;  when  it  is 
too  thick,  the  combustion  will  be  incomplete  for  want  of  sufficient  air. 

The  principal  causes  which  reduce  the  efficiency  of  the  furnace  of  a  boiler,  by  dimin- 
ishing the  temperature  of  the  products  of  combustion  and  the  total  heat  produced  by 
the  combustion  of  fuel,  are  the  following : 

I.  The  absorption  of  heat  by  incombustible  solid  matter  and  by  moisture  contained 
in  the  fuel. — The  proportion  of  incombustible  matter  in  coal  varies  from  If  to  26  per 
cent.  In  the  better  classes  of  English  semi-bituminous  coal  used  in  marine  boilers  it 
forms  from  6  to  12  per  cent,  of  the  fuel.  The  average  quantity  of  incombustible  matter 
contained  in  Pennsylvania  anthracite  is  16f  per  cent. 

Although  the  refuse  matter  has  a  high  temperature  when  it  is  removed  from  the  fur- 
nace, the  quantity  of  heat  thus  lost  is  small,  amounting  in  the  worst  cases  to  barely  one 


SEC.  13.  COMBUSTION.  49 

per  cent.  The  incombustible  matter  produces  a  more  injurious  effect,  especially  when 
it  fuses  easily  and  forms  clinker,  by  preventing  the  free  access  of  air  to  the  combustible 
portion  of  the  fuel.  The  principal  losses  due  to  the  presence  of  incombustible  matter 
are  connected  with  the  process  of  cleaning  the  fires,  and  will  be  referred  to  later. 

The  moisture  present  in  fuels  not  only  makes  latent  a  relatively  large  quantity  of 
heat  during  evaporation,  but  prevents  often  the  complete  oxidation  of  the  combustible 
portion  of  the  fuel. 

Wood,  when  newly  felled,  contains,  on  an  average,  40  per  cent,  of  moisture ;  after 
eight  or  twelve  months'  ordinary  drying  in  air  the  proportion  of  moisture  is  from  20  to 
25  per  cent.  (Itankine.) 

Coke,  being  of  a  porous  texture,  readily  attracts  and  retains  water  from  the  atmos- 
phere ;  and  sometimes,  if  it  is  kept  without  proper  shelter,  from  0.15  to  0.20  of  its 
gross  weight  consists  of  moisture.  (Rarikine.) 

The  quantity  of  moisture  absorbed  by  coal  varies  with  its  texture,  and  with  the 
duration  and  manner  of  its  exposure  to  dampness.  Hard  anthracites  absorb  only  a 
very  small  quantity  of  moisture. 

II.  Waste  ofunburnt  combustible  matter  in  the  solid  state.—  This  waste  depends  on 
the  behavior  of  the  fuel  during  the  process  of  combustion  and  on  the  care  and  skill  of 
the  fireman.     Anthracite  coal,  when  suddenly  heated,  splits  into  small  pieces,  and  dry 
bituminous  coal  is  converted  during  combustion  into  a  loosely  cohering  mass  of  small 
particles,  which  are  liable  to  fall  through  the  grate  when  the  fire  is  stirred  for  the  pur- 
pose of  removing  the  ashes.     In  cleaning  the  fire  a  small  quantity  of  coal  is  also  un- 
avoidably hauled  from  the  furnace  with  the  refuse.      "It  is  impossible  to  estimate 
the  greatest  amount  of  this  kind  of  waste  which  may  arise  from  careless  firing  ;  but  the 
amount  which  is  unavoidable  with  good  firing  has,  in  some  cases,  been  ascertained  by 
experiment  and  found  to  range  from  nothing  up  to  about  2£  per  cent."     (Rankine.} 

III.  Losses  arising  from  an  admission  of  excessive  quantities  of  air  to  the  fur- 
nace.—By  admitting  too  large  a  quantity  of  air  to  the  furnace  the  temperature  of  the 
products  of  combustion  is  decreased  and  their  mass  and  volume  are  increased  ;  the  effect 
of  this  is  a  reduction  of  the  rate  of  combustion,  the  loss  of  a  larger  quantity  of  heat 
present  in  the  escaping  chimney-gases,  and  sometimes,  when  the  furnace  temperature 
is  greatly  reduced,  the  incomplete  combustion  of  certain  gaseous  products  of  the  fuel. 
Too  large  a  calorimeter,  or  cross-area  of  the  passages  over  the  bridge-wall  or  through 
the  flues  relatively  to  the  rate  of  combustion,  favors  the  admission  of  an  excessive  quan- 
tity of  air.     The  proper  proportions  of  the  parts  of  a  boiler  will  be  considered  later. 

The  air  should  pass  in  thin,  evenly-distributed  streamlets  through  the  bed  of  fuel, 


50  STEAM  BOILERS.  CHAP.  II. 

or  it  should  enter  the  furnace  above  the  grate  in  the  form  of  numerous  fine  jets.  The 
admission  of  air  in  large  masses  is  always  injurious,  but  is  to  a  certain  extent  un- 
avoidable with  the  ordinary  methods  of  firing  ;  when  the  bed  of  fuel  is  too  thin  or  not 
evenly  distributed  over  the  grate,  and  whenever  the  door  is  opened  for  the  purpose  of 
throwing  fuel  on  the  grate,  or  levelling,  slicing,  and  cleaning  the  fire,  large  masses  of  air 
rush  into  the  furnace. 

When  the  fuel  is  not  evenly  distributed  over  the  grate,  the  air  rushes  with  great 
violence  and  in  large  masses  through  the  places  left  uncovered  or  insufficiently  covered, 
causing  the  phenomenon  of  "back-draught." 

When  the  combustion  is  forced  by  artificial  draught  the  lumps  of  coal  must  be 
smaller  and  the  bed  of  coal  must  be  thicker  than  with  natural  draught,  so  as  to  make 
the  interstices  between  the  lumps  smaller  and  the  route  of  the  air  through  the  bed  of 
coal  more  tortuous. 

The  following  is  the  result  of  "experiments  showing  the  effect  on  the  economic 
vaporization  of  admitting  an  increased  air-supply  through  the  grates  to  the  incan- 
descent coal  upon  them  by  carrying  thinner  fires."  "In  experiment  A  the  fires 
were  7  inches  thick,  and  in  experiment  D  they  were  less  than  half  that  thickness, 
the  grates  being  kept  just  covered.  The  rate  of  combustion  in  both  experiments  was 
sensibly  the  same,  and  very  slow,  being  6.498  pounds  of  the  combustible  portion  of 
anthracite  per  square  foot  of  grate-surface  per  hour  in  experiment  A,  and  6.149  pounds 
in  experiment  D. 

"The  economic  vaporization  in  experiment  A  was  11.8976  pounds  of  water  from  the 
temperature  of  212°  Pahr.  and  under  the  atmospheric  pressure,  per  pound  of  the  com- 
bustible portion  of  the  anthracite,  and  in  experiment  D  10.2716  pounds.  Hence  the 
admission  of  the  increased  air-supply  through  the  grates,  due  to  maintaining  a  very 
thin  fire  upon  them,  decreased  the  economic  vaporization  by  the  fuel 

/11.8976-  JHX2716\  IQO  =  13.667  per  centum."  (Report  of  Board  of  United  States 
\  11.8976  / 

Naval  Engineers  on  "  The  AsJicroft  Furnace-doors  and  Grate-bars"  March  27, 
1878.) 

The  loss  resulting  from  opening  the  furnace-door  is  avoided  or  lessened  by  using  a 
moving  grate,  to  which  the  fuel  is  supplied  by  mechanical  means  ;  or  by  using  vibrating 
or  rocking  grate-bars  for  removing  the  ash  and  clinker  from  the  fire.  The  former  have 
not  come  into  use  for  marine  boilers  ;  examples  of  the  latter  will  be  found  in  Chapter 
XIII. 

The  exact  amount  of  the  loss  in  vaporific  efficiency  of  coal  burnt  in  a  boiler-furnace, 


SEC.  13. 


COMBUSTION. 


51 


due  to  the  opening  of  the  door  for  the  purpose  of  removing  the  ash  and  clinker,  may  be 
deduced  from  the  experiments  made  by  the  Board  of  United  States  Naval  Engineers 
convened  to  determine  the  relative  value  of  the  Murphy  shaking-grate  and  of  the  com- 
mon grate  :  "  The  Murphy  apparatus  kept  the  fires  clean  and  free  of  holes,  crushed  the 
clinker  and  removed  all  the  refuse  from  the  furnaces  into  the  ashpits,  without  opening 
the  furnace-doors  for  such  purposes  and  without  using  fire-tools";  and  it  was  found 
"that  the  economic  gain  in  fuel  due  to  the  Murphy  grate  was  in  direct  proportion  to 
the  per  centum  of  refuse  removed  through  the  furnace-door,  as  appears  from  the  fol- 
lowing exhibit": 


Kind  of  coal  burnt. 

Per  centum  of  the  coal 
consumed  on  the  com- 
mon grate,  removed  as 
refuse  through  the 
furnace-door. 

Economic  gain  in  fuel 
by  the  Murphy  grate 
in  per  centum  of  the 
fuel  consumed  on  the 
common  grate. 

Bituminous  coal  lumps 

IO-9475 
I3-4338 
.    I9-3I47 

4-1529 
5-7417 
7.2972 

Bituminous  coal   dust. 

Anthracite  

"The  mean  of  the  three  determinations  gives  for  the  economic  loss  in  fuel  when 
burned  on  a  common  grate  0.3935  per  centum  of  that  fuel  for  every  one  per  centum  it 
contains  in  refuse  removed  through  the  furnace-door."  (Report  on  the  Murphy  Grate- 
bar  by  a  Board  of  United  States  Natal  Engineers,  June  25,  1878.) 

IV.  Waste  of  unburntfuel  in  the  gaseous  and  smoky  states. — The  complete  com- 
bustion of  coke,  hard  anthracite,  and  coals  containing  only  a  small  proportion  of  hydro- 
carbons presents  no  difficulty  as  long  as  the  thickness  of  the  bed  of  fuel  is  properly 
proportioned  to  the  draught,  and  a  small  quantity  of  air  enters  the  furnace  in  jets 
through  the  perforated  furnace-door  in  addition  to  the  quantity  passing  through  the 
grate. 

The  combustion  of  highly  bituminous  coal  presents  greater  difficulties.  Special  care 
has  to  be  taken,  in  the  design  of  the  boiler  and  in  the  management  of  the  fire,  that  the 
hydrocarbon  gases  distilled  from  the  coal  are  thoroughly  mixed,  at  a  sufficiently  high 
temperature,  with  the  proper  quantity  of  air.  A  greater  or  less  quantity  of  the  carbon 
contained  in  the  hydrocarbon  gases  remains  frequently  iinburnt,  forming  soot  or 
smoke ;  and  in  extreme  cases  the  fixed  carbon  contained  in  the  coal  is  alone  completely 
burnt. 

"If  smoke  is  mixed  with  carbonic-acid  gas  at  a  red  heat  the  solid  carbonaceous  par- 
ticles are  dissolved  in  the  gas  and  carbonic  oxide  is  produced.  This  is  the  mode  of 


52 


STEAM  BOILERS. 


CHAP.  II. 


operation  of  contrivances  for  destroying  smoke  by  keeping  it  at  a  high  temperature 
without  providing  a  sufficient  supply  of  air  ;  and  the  result  is  a  waste  instead  of  a  sav- 
ing of  fuel."  (Rankine.) 


TABLE  V. 

GENERAL  SYNOPTICAL  TABLE  OF  THE  CHARACTER   AND  EFFICIENCY  OF  AMERICAN  COALS,  BY 

W.  R.  JOHNSON. 


I 

2 

3 

4 

5 

6 

7 

8 

9 

10 

» 

12 

'3 

Designation  of  coal. 

Location  of  mine. 

Specific  gravity. 

Cubic  feet  of  space  required  to 
stow  a  ton. 

Volatile  combustible  matter  in 
100  parts. 

Fixed  carbon  in  100  parts. 

uj 

1 

8 

'fe 
1 

1 

Moisture  in  fuel  in  100  parts. 

Ratio  of  fixed  to  volatile  com- 
bustible matter. 

Rate  of  combustion  in  Ibs.  of  coal 
per  square  ft.  of  grate  per  hour. 

Percentage  of  waste  in  ashes 
and  clinker. 

Pounds  of  steam  from  water  at 
212°  per  pound  of  coal. 

Steam  from  212°  from  one  Ib. 
of  combustible. 

Beaver  Meadow,  Slope  No.  3. 
Beaver  Meadow,  Slope  No.  5. 

Pa. 
Pa. 
Pa. 

I.6IO 

I-55I 
.477 

40.78 
39-86 
j.1  71: 

2.38 

2.66 
•\  07 

88.94 
91.47 
OO  75 

7.11 

5-15 

4  41 

i-57 
0.72 

1.77 

37-37 

34-39 
20.56 

6.69 
6.27 
6.52 

11.96 
6.74 
6.Q7 

9.21 

9.88 

10.06 

10.462 
10.592 
10.807 

Pa. 

.464 

41.64 

2.06 

8o.O2 

6.13 

1.89 

30.00 

6.69 

6.97 

IO.II 

10.871 

Pa. 

.500 

JXX^O 

5.28 

8Q.I5 

5.56 

O.OI 

16.88 

6.95 

7.22 

8.93 

9.626 

Pa. 

.421 

45.82 

S.QI 

87.74 

2  OO 

22.44 

6.45 

8.93 

9-79 

10.764 

Lykens  Valley          

Pa. 

.389 

46.13 

6.SS 

83.84 

25 

OO3 

12.19 

6.92 

12.24 

9.46 

10.788 

New  York  and  Maryland) 

Md. 

-431 

41.71 

12.31 

73-50 

I2.4O 

1.79 

5-97 

6.28 

12.71 

9.78 

1  1.  2O8 

NefFs  Cumberland  

Md. 

•337 

41.26 

12.67 

74-53 

10.34 

2.46 

5-88 

7.86 

10.96 

9-44 

10.604 

Dauphin  and  Susquehanna  . 

Pa. 

Pa. 

-443 
.324 

44-32 

42.22 

13.82 
14.78 

74.24 
73.11 

11.49 
10.77 

0.45 
1.34 

5-37 
4-95 

6.86 
7-77 

16.36 
1  1.  20 

9-34 
9.72 

II.I7I 
10.956 

Pa. 

.388 

4O.45 

13.84 

71.53 

13.  06 

0.67 

5.16 

6.33 

16.92 

8.91 

10.724 

Cambria  County  

Pa. 

.407 

41.90 

20.52 

69.37 

9.15 

0.96 

6.68 

9-75 

9.24 

10.239 

Va. 

.294 

41.45 

29.86 

53.01 

14.74 

2.39 

1.78 

6.68 

14-83 

8.29 

9.741 

Pa. 

.252 

47.85 

36.76 

54.  Q3 

7.07 

1.24 

1.49 

8.25 

8.20 

8.942 

Ind. 

.273 

47.OI 

33.  QO 

58.44 

4-97 

2.60 

1.72 

11.09 

5.12 

7-34 

7-734 

IO662 

O.3O7 

15.87 

0.307 

4.60 

4.707 

SEC.  13. 


COMBUSTION. 


53 


TABLE  VI. 

GENERAL  SYNOPTICAL  TABLE  OF  THE  CHARACTER  AND  EFFICIENCY  OF  ENGLISH  COALS,  SHOWING 
THE  RESULTS  OF  THE  INVESTIGATIONS  OF  DE  LA  BECHE  AND  PLAYFAIR. 


I 

2 

3 

4 

5 

6 

7 

8 

9 

IO 

II 

12 

«3 

M 

2 

• 

1 

it 

n 

3 

5 

« 

o.  2 

c  t» 

i 

u 

1 

v  " 
•s'o 

1  - 

Locality  or  name  of  coal. 

$ 

i 

1 

1 

O 

•o 

II 

1-  • 

1 

o  e 
S2 
J>  „ 

1 

. 

O 

1 

1 

U 
X 

*~  o 

ill 

H  ;  T 

jj 

"5 

° 

E 

1 

3 

C 

o 

g 

0  J 

ill 

-  .  - 

! 

O  * 

1 

£ 

"3 

in 

5 

^ 

e 

^ 

1 

IJ 

M 

i" 

Welsh  Graigola  

Rt  R-J 

"       Anthracite  (Jones, 
Aubrev  &  Co.)..   ' 

1-375 

38.45 

04.07 
9144 

346 

0.21 

0.45 
0.79 

7.19 

2.58 

3-24 
1.52 

85.5 
92.9 

91-38 

6.12 

19.60 

13-563 
14.593 

9-35 
946 

"       Old  Castle   Fierv  , 

Vein   ..]' 

1.289 

43-99 

87.68 

4.89 

I-3I 

0.09 

3-39 

2.64 

79-8 

76.16 

6.02 

14.936 

8.01 

Binea  Coal   ... 

RR  f*h 

Llangenneck  

Rs  ifi 

4.03 

M3 

0.33 

1.03 

i't 

84.14 

7.65 

15-093 

9-94 

Pentrepoth  
Pentrefelin  

1-31 

88.72 

4.^0 
4.50 

1.O7 

0.18 

2.43 
3-24 

0.54 
3-36 

S3.O9 

82.5 

77-15 
79-  !4 

4-73 

14.260 

14.838 

8.86 
8.72 

Powel's  DufTrvn  .  .  . 
Mynydd  Xewvdd  .  . 
Cwm  Frood  Rock  ) 

1.326 

1.31 

42.09 
39-76 

.••:- 
.88.26 
'84.71 

3.72 
4.66 
5-76 

1.45 

1-77 

I.2I 

4-55 
0.60 
3-52 

3.26 
3.24 

84-3 
74-8 

81.04 
71.56 

5-52 
5-56 
2.91 

13.787 
15-092 
14.904 

6.36 
10.15 
9-52 

Vein  \ 

1-255 

40.52 

82.25 

5-^4 

i.  ii 

1.22 

3.S8 

6.00 

68.8 

62.80 

2.08 

14.788 

8.70 

Cwm  Nanty-gros.  .  . 
Pontv  Pool   .  .  . 

1.28 

40.00 

78.36 

5-59 

C   ftf* 

1.86 

3-01 

3-58 

5.60 

65.6 

60.00 

1.79 

13.932 

8.42 

Ebbw  Vale   

I  27> 

.     .    -, 

5.00 

2  16 

2-39 

4-3° 

5-52 

59.28 

1-73 

14.295 

747 

Porthmawr   Rock 

0.39 

1.50 

77-5 

3-59 

15-635 

IO.2I 

Vein  f 

1.39 

42.02 

74-70 

4-79 

1.28 

0.91 

3.60 

14.72 

63.1 

48-18 

1-37 

12.811 

7-53 

Scotch    Dalkeith    Jewel  ) 

Seam  i' 

1.277 

44.98 

74-55 

5.14 

O.IO 

0.33 

I5-5I 

4-37 

49-8 

4543 

1.24 

12.313 

7.08 

"       Dalkeith  Corona-  ; 

tion  Seam  i' 

1.316 

43-36 

76.94 

5.20 

Trace 

0.38 

14-37 

3-io 

53-5 

50.40 

1.14 

12.772 

7-71 

"       Fordel  Splint  

1  25 

7n  cfi 

T    tf, 

Q   «a 

1.13 

O-33 

52.O3 

45.O3 

13.817 

7.56 

STEAM  BOILERS. 


CHAP.  IL 


w 
j 

M 


§ 

S 

iff 

§ 


00 


«  ^ 
n    w 


tn 

O  S 

W  ^ 

U  W 

<  o 

H  £ 

W  J 

U  U 

S  S 


o  >• 

as,  > 

•-  < 

i  1 

oa  5 

«  < 

<J  ^ 

s  i 

H  ^ 

O  pd 

tn  ~ 

*  H 

o  t: 

u  * 


i§ 


S- 

5 

0. 

U 

h 
O 
tn 

iJ 


7. 


X 

3 


S  ^ 

PH  W 

s  s 

«  o 

O  a 

f5  ° 


O 

a 
c« 


o  )ooj  ajBnbs  jad  JIKHJ 
ja  aiqijsnquiOD  jo  spunod  ui 
uoijsnqiuoD  jo  3)BJ  uiniuixu'i 


^.  y  t 

o  « 


P- 

II; 

Bigj 
I 


- 

- 


S  o  „  B  a. 
.H^-a  U3 

iijhS|» 

K  a  «  p,£.^ 

iSii1! 

liSfSl 


i 


Q.  Q. 


•uoijsnquioD  jo 
ajEJ  AVOIS  auj  iv 


-snqraoo  jo  S 

umjpaui 


-snquioo  jo  3jej 
uiniuixEUiaqi  jy 


'uoijsnquioo  jo 
ajEJ  A\O[S  auj  jy 


-snqraoD  joa 


•flop 


=41  'V 


-snqtuoa  jo  SJBJ 
uinuaixELU  aqi  )y 


•]3Hj  jo  uoiuod  3|qilsnaiuOD 
jo  *q|  j.nt  oanss.ud  ouaqasoui 
-IE  43pun  -j  Otlt  jo'j3je\\  jo 

'Sq[    UI 


qsy 


5    1  §   & 
:    rt   .j  c» 


*  -      **  *fi. 

NO  CJ) 

p       r^  efl 

l/>          M  O 

••»      «  n 


CTl       >O  S         M 

«     M     d     d 


11 
odd 


. 

M               B       B*       19  10  & 

«T              ^      *O         IO  1O  OS 

CTi              CTl        O         O  0\  00 


a          1  f  S 

\d  od     od      t^ 


in     o» 

CO         t% 


* 


"S    f  J  5 


D,  * 

H       0 


K    R    if    &    8 
«   «i  «s 


n    A  &  <fi  d 

d     d  M  d  d 

aw  QO  M  o 

d      d  -  H  S 


^2 
S 


K  S 

a   s 


~    8,   8.   g 


3, 

a 


s  a  ft  !? 

eft      •»      •*      -* 


S 


u_ 

7T 


O         CO 

\is    S 

*  * 


CHAPTER  in. 

TRANSMISSION  OF  HEAT  AND   EVAPORATION. 

1.  Laws  of  Transmission  of  Heat. — All  bodies  transfer  heat  to  the  surrounding 
cooler  bodies  till  their  temperature  becomes  equalized. 

The  quantity  of  heat  transferred  from  one  body  to  another  depends  on  the  difference 
of  their  temperatures  and  their  respective  specific  heat,  and,  in  case  the  molecular  con- 
dition of  one  or  both  bodies  is  changed,  on  their  respective  latent  heat. 

The  rate  at  which  the  transfer  takes  place  between  two  bodies  depends,  first,  on  the 
degree  and  the  difference  of  their  temperatures ;  secondly,  on  the  extent  of  surface 
transmitting  and  receiving  heat ;  thirdly,  on  the  nature  of  the  material  of  the  bodies, 
and  on  the  condition  of  their  surfaces  ;  fourthly,  on  the  nature  and  thickness  of  the  in- 
tervening substances. 

There  are  three  processes  by  which  heat  is  transferred,  called  respectively  radiation, 
conduction,  and  convection. 

Radiation,  is  the  exchange  of  heat  by  direct  rays  between  bodies  not  in  contact,  and 
takes  place  at  all  temperatures  and  at  any  distance  through  space. 

These  rays  produce  the  phenomena  of  heat  only  in  bodies  which  intercept  them  more 
or  less  completely.  Gases  intercept  and  emit  heat-rays  very  feebly ;  most  solids  and 
fluids,  on  the  contrary,  intercept  and  emit  these  rays,  which  are  either  wholly  absorbed 
or  partly  reflected  by  them.  The  rate  of  transmission  of  heat  by  radiation  between 
two  bodies  is  increased  by  making  their  surfaces  dark  and  rough,  and  diminished  by 
smoothing  and  polishing  them.  In  the  steam  boiler  the  radiation  from  the  solid  incan- 
descent fuel  is  far  greater  than  from  the  carbonaceous  flame,  while  the  transparent  hot 
gases  scarcely  radiate  any  heat  at  all. 

Conduction  is  the  transfer  of  heat  between  bodies  in  contact,  and  is  distinguished  as 
external  and  internal  conduction,  accordingly  as  it  takes  place  between  two  distinct 
bodies,  or  between  the  parts  of  one  continuous  body. 

Convection  is  the  diffusion  of  heat  in  a  fluid  mass  by  means  of  the  circulation  and 
mixture  of  the  particles  of  that  mass.  The  most  rapid  convection  of  heat  is  effected  by 
means  of  cloudy  vapor,  which  combines  the  mobility  of  a  gas  with  the  comparatively 

55 


56  STEAM  BOILERS. 


CHAP.  III. 


greater  conducting  power  of  a  liquid.     Convection  is  the  only  process  that  can  be  de- 
pended upon  for  the  rapid  distribution  of  heat  throughout  a  mass  of  water. 

The  rate  of  internal  conduction  in  a  solid  body  depends,  first,  on  the  variation  of 
temperature  along  a  line  perpendicular  to  the  section  through  which  the  heat  is  trans- 
ferred, and,  secondly,  on  the  coefficient  of  internal  conductivity  of  the  substance  in 
question.  Although  this  coefficient  varies  slightly  with  different  temperatures,  it  may 
be  considered  practically  as  constant  for  the  same  substance.  Designating  the  number 
of  thermal  units  transmitted  through  a  square  foot  of  area  per  hour  by  Q, 
the  temperatures  of  the  two  sides  of  a  substance  by  T  and  Ta 

the  rate  of  conduction  through  a  plate   of  the  thickness  t,  in   inches,  may  be  ex- 
pressed by  the  equation  : 


where  p  may  be  called,  according  to  Rankine,  the  coefficient  of  thermal  resistance. 
The  value  of  this  coefficient  for  various  substances  is  as  follows  :  copper  =  0.0018  ; 
iron  =  0.0043*  ;  zinc  =  0.0045  ;  lead  =  0.0090  ;  marble  and  calcareous  deposits  = 
0.0716;  brick  =  0.1500. 

When  a  plate  consists  of  layers  of  different  substances,  its  total  internal  thermal 
resistance  may  be  found  by  adding  together  the  resistances  of  the  several  layers  ;  in 

rp  _  m 

such  a  case  equation  [I.]  assumes  this  form:  Q  =  ~  —  fi.     [la.] 

-^  p  t 

*  "  Principal  Forbes  .  .  .  has  likewise  determined  the  absolute  conductivity  of  wrought-iron.  In  his  experi- 
ments conductivity  was  expressed  in  terms  of  the  amount  of  heat  as  unity  which  is  required  to  raise  the  temperature 
of  one  cubic  foot  of  water  by  one  degree  centigrade.  He  expresses  the  amount  of  heat  reckoned  in  such  units  which 
would  traverse  in  one  minute  across  an  area  of  one  square  foot  a  plate  of  iron  one  foot  thick  with  the  two  surfaces 
maintained  at  temperatures  differing  by  one  degree  centigrade.  According  to  these  experiments,  the  conductivity  at 
0°  C.  of  one  of  his  bars  was  .01337,  while  that  of  another  bar  was  only  .00992.  This  discordance  was  probably  due  to 
a  difference  in  the  quality  of  the  iron  of  the  two  bars."  (Balfour  Stewart,  "An  Elementary  Treatise  on  Heat.") 

The  larger  result  was  obtained  with  a  square  bar  1}  ins.  thick,  the  smaller  one  with  a  square  bar  1  inch  thick. 
In  either  case  the  conductivity  diminished  as  the  temperature  increased.    In  the  larger  bar, 
the  conductivity  at  100°  C.  was  24.3  per  cent,  less  than  at    0°  C. 

"  200°  C.    "    13.4        "  "  100°  C. 

"  275°  C.    "      8.6        "  "  200°  C. 

In  the  smaller  bar  "  100°  C.    "    15.8        "  "  0°  C. 

"  200°  C.    "      8.5        "  "  100°  C. 

"  275°  C.    "      5.2        "  "  200°  C. 

Professor  Tait  has  given  reasons  for  believing  that  the  thermal  conductivity  of  metals  may  be  inversely  proportional 
to  their  absolute  temperature. 


SBC.  8.  TRANSMISSION  OF  HEAT  AND  EVAPORATION.  57 

The  rede  of  external  conduction  between  a  solid  body  and  a  fluid  may  be  expressed 
by  dividing  the  difference  of  their  temperatures  by  a  coefficient  of  external  resistance, 
depending  on  the  nature  of  the  substances,  the  condition  of  their  surfaces,  and  also  on 
their  temperatures.  Designating  the  value  of  these  coefficients  for  the  two  surfaces 
of  a  given  plate  by  a  and  al ,  the  quantity  of  heat-units  transmitted  per  square  foot 
of  surface  per  hour,  from  one  fluid  to  another,  through  a  plate  t  inches  thick,  may 

T—  T 

be  expressed  by  the  formula :   Q  =  —*— .     [II.  ] 

G -j-  ffl-r  pi 

2.  Experiments  on  the  Transmission  of  Heat  by  Isherwood. — Careful  ex- 
periments on  the  heat-conducting  power  of  different  metals  were  made  by  Isherwood  in 
1867  at  the  Washington  Navy- Yard.  The  metals  experimented  upon  were  pure,  refined 
copper,  brass  consisting  of  60  parts  of  copper  and  40  parts  of  zinc,  rolled  wrought-iron 
of  the  best  quality,  and  ordinary  cast-iron  which  had  had  several  remeltings.  Cylin- 
drical pots  of  these  metals,  10  inches  in  inside  diameter  and  21i  inches  in  inside  height, 
were  immersed  in  a  common  cylinder,  which  was  well  protected  by  a  non-conducting 
material  and  supplied  with  steam  of  a  certain  temperature  and  pressure  from  a  large 
boiler.  The  pots  were  kept  filled  with  water  of  212°  temperature  by  a  steady  supply 
from  separate  tanks,  and  the  quantity  of  this  water  evaporated  by  the  heat  supplied 
by  the  steam-bath  measured  the  thermal  conductivity  of  the  respective  metals  ;  hence, 
"exactly  the  same  temperature  was  upon  the  entire  exterior  surface  of  all  four  pots, 
while  the  water  inside  the  pots  was  vaporized  under  identical  hygrometrical  and  baro- 
metrical conditions  of  the  atmosphere.  Each  experiment  consisted  of  from  54  to  108 
hours,  nine  hours  of  each  day  being  devoted  to  it."  Great  care  was  exercised  to 
maintain  the  temperatures  equal  throughout  each  experiment,  and  all  conditions  were 
noted  every  15  minutes  in  a  tabular  log.  "  Each  series  of  experiments  was  exactly 
repeated  on  pots  of  three  thicknesses  of  metal — viz.,  £,  J,  and  f  inch — with  the  view 
of  ascertaining  whether  the  vaporizing  efficiency  of  the  metals  was  affected  by  their 
thickness. 

"  With  each  thickness  of  metal  twenty  experiments  were  made,  the  temperature  of 
the  steam  increasing  by  5°  Fahr.  from  220°  Fahr.  for  the  first  to  320°  Fahr.  for  the  last 
experiment.  All  the  pots  were  turned  and  bored  to  exactly  the  same  dimensions. 

"For  each  experiment  there  was  calculated  the  number  of  pounds  of  water  vaporized, 
from  the  temperature  of  212°  Fahr.  and  under  the  standard  atmospheric  pressure  of 
29.92  inches  of  mercury,  by  each  pot ;  and  the  heat-conducting  powers  of  the  metals 
were  considered  to  be  in  the  ratio  of  those  weights.  The  following  are  the  general 
results : 


58 


STEAM  BOILERS. 


CHAP.  III. 


"1ST.  All  other  things  equal,  the  weight  of  water  vaporized  in  a  given  time  was  in 
the  direct  ratio  of  the  difference  of  the  temperatures,  inside  and  outside  of  the  pots. 

"2r>.  All  other  things  equal,  the  weight  of  water  vaporized  in  a  given  time  was  not 
affected  by  the  thickness  of  the  metal.  The  rate  of  vaporization  was  exactly  as  great 
from  the  f -inch  thick  metal  as  from  the  f-inch  thick  metal. 

"3D.  The  following  are  the  fractions  of  a  pound  of  water  vaporized  per  hour  from  each 
square  foot  of  the  interior  surface  of  the  pots,  from  the  temperature  of  212°  Fahr.  and 
under  the  standard  atmospheric  pressure  of  29.92  inches  of  mercury,  by  a  difference  of 
temperature  of  one  degree  Fahrenheit  between  the  inside  and  the  outside  of  the  pots. 

"  These  are  the  absolute  heat-conducting  powers  of  the  metals  named"  —viz.  : 


Thermal  conductivity  m 
terms  of  fractions  of  a 
pound  of  water  of    212° 
vaporized  under 
atmospheric  pressure. 

Thermal  conductivity  in 
terms  of  heat-units 
transmitted    per    hour 
through  one  square  foot 
of  material  by  difference 
of  temperature  of 
i°  Fahr. 

Relative  thermal  conduc- 
tivity. 

CoDDer.  . 

0.665365 
0.576610 
0.386895 
0.326956 

642.543 
556.832 
373-625 
3I5-74I 

I.OOOOOO 
0.866607 
0.581478 
0.49*393 

Wrought-iron  

Ccist-iron  

3.  Experiments  on  the  Transmission  of  Heat  by  P6clet. — The  results  of 
the  foregoing  experiments  agree  pretty  closely  with  those  obtained  by  former  investi- 
gators, as  far  as  the  relative  thermal  conductivity  of  these  metals  is  concerned ;  the 
absolute  values  obtained  are,  however,  much  smaller  than  those  found  by  Peclet.  The 
latter' s  experiments  prove  that  the  rate  at  which  fluids  transmit  heat  to,  and  absorb 
heat  from,  solid  bodies,  depends— other  conditions  being  equal — greatly  on  the  more  or 
less  perfect  circulation  of  the  fluids,  so  that  each  particle  of  fluid  is  at  once  replaced  by 
other  particles  as  soon  as  it  has  absorbed  or  parted  with  some  heat  by  contact  with  the 
solid.  On  this  account  Peclet  used  water  instead  of  steam  as  the  source  of  heat  in  his 
experiments,  because,  by  the  condensation  of  the  latter,  a  film  of  water  is  deposited  on, 
and  clings  tenaciously  to,  the  walls  of  the  experimental  vessel ;  and  he  produced  rapid 
circulation  in  the  heat-absorbing,  as  well  as  in  the  heating,  medium  by  mechanical  means. 
By  observing  such  precautions  Peclet  obtained  results  which  are  in  accordance  with 
the  law  that  the  quantity  of  heat  transmitted  through  a  solid  body  in  a  unit  of  time 
diminishes  in  the  direct  ratio  of  the  increase  of  thickness. 

Peclet' s  experiments  on  the  cooling  of  vessels  when  exposed  to  the  air,  the  circula- 
tion of  the  latter  being  produced  simply  by  the  effect  of  the  transmitted  heat,  proved 


SBC.  4.  TRANSMISSION  OP  HEAT  AND  EVAPORATION.  59 

that,  when  the  walls  of  the  experimental  vessel  were  covered  by  pulverulent  deposits, 
the  quantity  of  heat  transmitted  in  a  unit  of  time  was  independent  of  the  internal  ther- 
mal conductivity  of  the  metal  and,  within  the  limits  of  ordinary  practice,  of  the  thick- 
ness of  the  walls,  but  depended  greatly  on  the  form  of  the  vessel  and  increased  in  a 
certain  ratio  with  the  difference  of  temperature  ;  both  these  latter  elements  affecting  the 
rapidity  of  the  circulation  of  the  air. 

4.  Transmission  of  Heat  in  a  Steam  Boiler.  —  Since  in  a  steam  boiler  the  heat- 
ing-surfaces become  soon  covered  with  deposits  of  scale,  rust,  and  soot,  while  the  cir- 
culation of  the  hot  gases  on  one  side  and  of  the  water  or  steam  on  the  other  side  is 
more  or  less  imperfect,  the  evaporative  power  of  these  surfaces  may  be  considered, 
within  the  limits  of  ordinary  practice,  as  independent  of  the  thickness  and  kind  of  the 
metal  used,  but  depending  principally  on  their  form  and  position,  on  the  condition  of 
their  surfaces,  and  on  the  difference  of  the  temperatures  to  which  the  opposite  sides 
are  exposed. 

Rankine  expresses  the  total  thermal  resistance  of  the  plates  and  tubes  of  a  steam 

boiler  by        ffl       ;   substituting  this  expression  for  the  divisor  a  -f  fft+  P  t,  equation 

•*-       *« 
[II.  ]  assumes  the  form  : 


a 

The  numerical  value  of  a  lies  between  160  and  200.  This  formtila  is  not  intend- 
ed to  give  more  than  a  rough  approximation  ;  in  fact,  the  varying  conditions  obtaining 
in  a  steam  boiler  preclude  the  possibility  of  an  accurate  theoretical  determination  of  its 
coefficient  of  thermal  resistance. 

To  ensure  the  proper  circulation  of  the  water  to  which  heat  is  to  be  transmitted  two 
conditions  must  be  observed  —  viz.,  first,  the  heat  must  be  applied  to  the  bottom  of  the 
vessel  containing  the  water,  so  that  the  latter,  as  it  becomes  lighter  by  being  heated, 
may  ascend,  being  displaced  by  a  descending  column  of  heavier,  colder  water  ;  second- 
ly, the  heating-surfaces  must  have  such  a  shape  and  position  as  to  permit  the  free 
escape  of  the  heated  water  and  steam. 

As  long  as  the  clean  surface  of  a  boiler-plate  is  in  contact  with  solid  water  the  most 
intense  heat  of  the  furnace  may  be  applied  to  the  other  side  without  overheating  the 
plate  ;  when,  on  the  contrary,  a  plate  is  in  contact  with  steam,  it  will  soon  assume  the 
temperature  of  the  hot  gases  to  which  the  other  side  is  exposed.  This  great  heat- 
absorbing  capacity  of  water  is  owing  to  three  catises  :  first,  its  thermal  conductivity  is 
greater  than  that  of  gases  ;  secondly,  its  specific  heat  is  more  than  twice  as  great  as 


OF    THE 

UNIVERSITY 

OF 


60  STEAM  BOILERS.  CHAP.  III. 

that  of  steam ;  and,  thirdly,  a  large  quantity  of  heat  becomes  latent  during  evapo- 
ration. 

5.  Efficiency  of  Heating-surfaces  in  a  Steam  Boiler. — The  efficiency  of  a 
heating-surface  may  be  measured  by  the  ratio  borne  by  the  amount  of  heat  transmitted 
by  it  to  the  total  amount  of  heat  available  for  transmission.  This  efficiency  in  a  steam 
boiler  depends  on  the  following  conditions :  first,  the  proportion  which  the  extent  of 
the  surfaces  receiving  and  transmitting  heat  bear  to  the  volume  of  hot  gas  bounded  by 
them ;  secondly,  the  difference  of  temperatures  of  the  hot  gas  on  the  one  side  of  the 
plates,  and  of  the  water  or  steam  on  the  other  side ;  thirdly,  the  time  allowed  for  the 
transmission  of  heat ;  fourthly,  the  nature,  condition,  and  thickness  of  the  plates 
forming  the  heating-surfaces ;  fifthly,  the  position  and  shape  of  the  plates ;  sixthly, 
the  nature  of  the  heating  and  heat-absorbing  media. 

The  following  interesting  experiment  on  the  influence  of  the  position  of  heating- 
surfaces  on  their  efficiency  is  recorded  by  Tredgold :  "  Mr.  Armstrong  found  that  a 
cubical  metallic  box,  submerged  in  water  and  heated  from  within,  generated  steam  from 
its  upper  surface  more  than  twice  as  fast  per  unit  of  area  than  it  did  from  the  sides 
when  vertical,  and  that  the  bottom  yielded  none  at  all..  These  remarkable  differences 
are  owing  to  the  difficulty  with  which  steam  separates  from  a  vertical  surface  to  give 
place  to  fresh  charges  of  water,  and  to  the  impossibility  of  leaving  the  inverted  surface 
at  all.  By  slightly  inclining  the  box  the  elevated  side  much  more  easily  parted  with 
the  steam,  and  the  rate  of  evaporation  was  increased ;  while  on  the  depressed  side  the 
steam  hung  so  sluggishly  as  to  lead  to  an  overheating  of  the  metal." 

In  the  marine  steam  boiler  the  temperature  of  the  gases  in  the  furnace  ranges  pro- 
bably between  1,500°  and  2,500°  ;  and  when  these  gases  enter  the  chimney  their  tempe- 
rature has  been  reduced  to  from  450°  to  650°. 

On  the  other  hand,  the  temperature  of  the  steam,  and  consequently  of  the  water, 
ranges  between  250°  and  350°,  according  to  the  steam-pressure  used.  Since  the  water  is 
introduced  into  the  boiler  at  a  much  lower  temperature,  varying  ordinarily  between 
100°  and  120°,  there  would  be  theoretically  a  decided  gain  in  the  heating  efficiency  if 
the  water  entered  the  boiler  at  the  point  where  the  hot  gases  have  the  lowest  tempera- 
ture. Such  an  arrangement  is,  however,  rarely  made  in  marine  boilers,  on  account  of 
mechanical  difficulties  connected  with  it. 

The  plates  forming  the  furnace  of  a  marine  boiler  transmit,  relatively,  by  far  the 
greatest  amount  of  heat  to  the  water ;  for,  in  addition  to  the  effect  produced  by  the 
high  temperature  of  the  evolved  gases  in  contact  with  the  sides  and  the  top  of  the  fur- 
nace, the  radiation  of  heat  from  the  incandescent  solid  fuel  is  of  considerable  impor- 


SEC.  5.  TRANSMISSION  OP  HEAT  AND  EVAPOEATION.  61 

tance.  Peclet  states  that  the  quantity  of  heat  radiated  from  incandescent  carbon,  freely 
suspended,  is  at  least  one-half  of  its  total  heat  of  combustion.  In  the  furnace,  how- 
ever, only  the  upper  surface  of  the  fuel  radiates  heat  directly  to  the  water-heating  sur- 
faces. The  rays  of  heat  emitted  through  the  open  spaces  of  the  grate  are  mostly  ab- 
sorbed by  the  ashes  ;  but  this  heat,  as  well  as  that  received  by  the  furnace-door,  is  to  a 
great  extent  reabsorbed  by  the  entering  air. 

In  the  combustion-chamber  or  back-connection  the  temperature  of  the  products  of 
combustion  is  probably  fully  as  high  as  in  the  furnace,  since  the  thorough  mixing  of 
the  hot  gases  with  the  air  completes  their  combustion.  The  radiation  of  heat  from  the 
carbonaceous  flame  is  likewise  frequently  of  much  importance  at  this  part  of  the 
boiler. 

Isherwood  states,  as  the  result  of  experiments  on  marine  boilers,  that  of  the  evapo- 
ration of  water  in  well-proportioned  tubular  boilers  about  55  per  cent,  is  due  to  the 
furnace  and  back-connection,  while  the  heating-surface  contained  in  those  parts  is  only 
about  20  per  cent,  of  the  total  heating-surface  of  the  boiler. 

On  leaving  the  combustion-chamber  or  back-connection  the  gases  pass  generally  be- 
tween or  into  numerous  tubes.  By  subdividing  in  this  manner  the  gaseous  mass  into  a 
great  number  of  streamlets  the  proportion  of  heating-surface  to  volume  of  gas  for  a 
given  length  is  greatly  increased,  and  the  absorption  of  heat  takes  place  rapidly. 

When  the  hot  gases  pass  through  horizontal  tubes  the  upper  side  of  them  is  most 
effective  as  a  heating-surface,  since  on  the  inside  it  is  kept  relatively  clean  of  sooty  de- 
posits and  the  hottest  gases  come  in  contact  with  it,  while  at  the  same  time  the  steam- 
bubbles  escape  most  freely  from  that  portion  of  the  tubes.  Only  such  portions  of  the 
hot  gases  as  come  in  actual  contact  with  the  heating-surfaces  impart  their  heat  to  them. 
In  internally-heated  horizontal  tubes  the  outer  film  of  the  hot  gases  descends  as  soon 
as  it  has  parted  with  some  of  its  heat ;  in  this  manner  the  temperature  of  the  current 
is  equalized  to  some  extent  by  convection  of  heat.  Some  writers  ascribe  the  smaller 
efficiency  of  internally-heated  vertical  tubes  to  the  fact  that  the  outer  film  of  gases  in 
contact  with  the  metal  has  no  tendency  to  mingle  with  the  central  portion  of  the  cur- 
rent, while  at  the  same  time  the  steam-bubbles  generated  at  the  lower  end  of  the  tube 
continue  to  envelop  the  tube  as  they  rise. 

On  account  of  the  great  difference  in  temperature  of  the  gases  as  they  enter  and 
leave  the  tubes,  the  heating  power  of  the  tubes  decreases  rapidly  toward  the  chimney- 
end.  According  to  formula  [III.]  of  this  chapter  the  quantity  of  heat  transmitted  varies 
directly  as  the  square  of  the  difference  of  temperature  at  the  two  sides  of  a  plate  :  in 
practice  the  efficiency  of  the  tube-surface  diminishes  at  a  still  greater  rate,  on  account 


62  STEAM  BOILERS.  CHAP.  III. 

of  the  greater  accumulation  of  soot  and  scale  at  the  chimney-end  of  the  tubes.  On  the 
other  hand,  it  must  be  observed  that  the  same  cause  which  produces  the  greater  deposi- 
tion of  soot — viz.,  the  diminished  velocity  of  the  gases  (the  volume  of  which  decreases 
proportionally  with  the  temperature,  while  the  area  of  the  tubes  remains  constant)— 
allows  the  gases  also  to  remain  a  longer  time  in  contact  with  the  heating-surfaces. 

Isherwood  suspended  various  metals,  the  melting-points  of  which  are  well  known, 
at  different  points  in  the  chimney-ends  of  horizontal  fire-tubes,  and  found  that  the  tem- 
perature of  the  discharged  gases  is  considerably  higher  at  the  upper  than  at  the  lower 
rows  of  tubes  in  the  same  boiler ;  he  estimates  that  this  difference  of  temperature  is  at 
times  as  high  as  300°.  This  difference  is  probably  due  partly  to  the  tendency  of  the  hot- 
test gases  to  rise  to  the  highest  point,  partly  to  the  fact  that  the  mass  of  rising  steam- 
bubbles  envelops  the  upper  tubes  to  a  greater  or  less  extent,  while  the  lower  tubes  are 
surrounded  by  a  more  solid  body  of  water. 

When  the  gases  enter  the  front  smoke-connection,  or  uptake,  in  their  passage  to  the 
chimney,  their  temperature  must  be  reduced  to  a  sufficiently  low  degree  to  cause  no  in- 
jury to  the  metal  plates  of  the  boiler,  as  these  are  no  longer  in  contact  with  water,  but 
with  steam  or  air.  Sometimes  special  provisions  are  made  to  utilize  some  of  the  heat 
of  the  escaping  gases  in  superheating  or  drying  the  steam,  by  keeping  them  in  contact 
with  extensive  surfaces  surrounded  by  the  steam. 

6.  Loss  of  Efficiency  of  Boilers  by  External  Radiation  and  Conduction.— 
The  heat  radiated  from  the  incandescent  coal  through  the  openings  of  the  furnace-door 
and  through  the  interstices  of  the  grate  is  almost  completely  reabsorbed  by  the  enter- 
ing air.  The  temperature  of  the  gases  in  the  chimney  is  reduced  to  some  extent  by  the 
radiation  and  conduction  of  heat  from  the  smoke-pipe,  and  the  draught  of  the  boiler  is 
correspondingly  diminished ;  but  the  loss  due  to  this  cause  is  trifling  in  large  boilers. 

The  loss  of  heat  due  to  radiation  and  conduction  from  the  shell  of  marine  boilers 
may  be  reduced  to  a  small  amount  by  covering  the  shell  with  non-conductive  materials, 
and  by  forming  a  dead-air  space  between  the  shell  of  the  boiler  and  its  covering. 

The  loss  of  heat  by  radiation  and  conduction  from  steam  boilers,  pipes,  etc.,  has 
been  determined  by  experiments  made  in  the  years  1863-65,  under  the  direction  of  the 
Bureau  of  Steam  Engineering  of  the  United  States  Navy  Department,  which  have  been 
described  and  analyzed  by  Chief -Engineer  Isherwood,  U.S.N.,  in  the  Journal  of  the 
Franklin  Institute,  March,  1878. 

The  radiator  used  in  these  experiments  was  a  flat  box  constructed  of  plate-iron  ^ 
inch  thick.  "  The  covering  employed  was  the  ordinary  cow-hair  felt,  manufactiared  for 
clothing  steam  boilers,  weighing  one  pound  per  square  foot  when  1£  inches  thick.  It 


SEC.  6. 


TRANSMISSION  OF  HEAT  AND  EVAPORATION. 


63 


was  stitched  tightly  over  the  radiator  so  as  to  be  in  contact  at  all  points,  thereby  pre- 
venting air-spaces,  or  air  circulation,  between  the  felt  and  the  radiator."  The  thickness 
of  the  felt  covering  used  in  the  experiments  varied  from  J  inch  to  7£  inches. 

The  experiments  were  made  with  steam-pressures  varying  between  10  and  60  pounds 
per  square  inch  above  the  atmosphere,  and  the  results  showed  that  in  still  air,  "ceteris 
paribus,  within  the  limits  of  the  experimental  temperatures,  the  quantity  of  heat 
radiated  in  equal  times  from  the  same  surface  with  different  temperatures  on  its  op- 
posite sides  was  in  the  direct  ratio  of  their  difference." 

By  plotting  the  mean  final  results  for  each  set  of  experiments  it  was  shown  that  the 
units  of  heat  radiated  per  hour  per  square  foot  of  surface  per  degree  Fahrenheit  diffe- 
rence of  temperature  on  the  opposite  sides  of  the  surface,  varied  almost  exactly  "in  the 
inverse  ratio  of  the  square  roots  of  the  thicknesses  of  felt  employed,  from  the  thickness 
of  7|  inches  up  to  the  thickness  of  1  inch,  from  which  latter  thickness  up  to  naked 
metal  the  curve,  though  a  fair  one,  followed  no  regular  law." 


Thickness  in  inches  of 
the  cow-hair  felt  on  the 
air  side  of  the  boiler-plate 
iron. 

Number  of  Fahrenheit  units  of  heat  lost  per  hour  per 
square  foot  of  boiler-plate  iron,  5-16  inch  thick,  per  degree 
Fahrenheit  difference  of  temperature  between  that  of  the 
steam  on  one  side  of  the  metal  and  that  of  the  still  air  upon 
the  opposite  side. 

Naked 
0.25 
0.50 

o-7S 

I.OO 

1-25 
1-50 

2.9330672000 
1.0540710250 
0.5728646875 
0.4124625750 

0-3070554725 
0.2746387609 
0.2507097171 

Two  experiments,  each  lasting  72  consecutive  hours,  were  made  to  determine  the 
effect  of  covering  the  boiler  with  felt  on  the  economic  evaporation,  at  the  Navy- Yard, 
New  York,  in  October,  1863,  and  are  described  by  Isherwood  in  "Experimental  Re- 
searches," Vol.  II.  The  experimental  boiler  was  of  the  locomotive  type,  and  had  5.3066 
square  feet  of  grate-surface,  22.1  cubic  feet  of  water-room,  and  12.2  cubic  feet  of  steam- 
room.  The  boiler  stood  in  a  shed  of  rough  boards  with  one  end  open  ;  the  circulation 
of  air  around  it  was  consequently  considerably  greater  than  would  have  been  under 
the  decks  of  a  vessel.  The  experiments  consisted  in  determining  the  economic  evapo- 
ration of  the  boiler  when  covered  with  thick  felt  and  when  not  covered,  the  condi- 
tions of  the  trials  being  otherwise  as  nearly  as  possible  alike.  The  results  of  these  ex- 
periments are  summed  up  by  Isherwood  as  follows  : 


(J4  STEAM  BOILERS.  CHAP.  III. 

"  The  number  of  pounds  of  water  evaporated  per  hour  during  the  experiment  with 
the  boiler  not  covered  with  felt  was  (-  ^-^ — ?=  1  687.565  ;  and  as  we  have  seen  that  the 

addition  of  felt  effected  a  saving  of^22.05  per  centum  of  this  quantity,  we  have  (687.565 
X  0.2205  —)  151.608  pounds  of  steam  condensed  per  hour  by  its  omission.  The  exter- 
nal surface  of  the  boiler  from  which  heat  was  radiated  was  94.09  square  feet,  conse- 
quently (-— ' '--^= \  1.6113  pounds  of  steam  were  condensed  per  hour  per  square  foot 

\   */4.  Ut/         / 

of  unfelted  surface.  The  temperature  of  the  water  and  steam  within  was  267°  Fahr., 
and  of  the  external  atmosphere  53.5°.  The  thickness  of  the  boiler-plate  was  one-quar- 
ter inch." 

The  writer  also  calls  attention  to  the  fact  that  the  per  centum  of  condensation  due  to 
radiation  from  the  external  surface  of  the  boiler  will  be  greatly  less  for  large  boilers 
"  and  in  proportion  to  size,  because,  while  for  similar  boilers  the  external  surface  in- 
creases as  the  square  of  any  dimension,  the  contents  increase  as  the  cube  of  the  same 
dimension,  and  the  steam -producing  capability  is  as  the  contents." 

7.  Efficiency  of  Boilers. — The  efficiency  of  a  boiler  is  measured  by  the  ratio 
borne  by  the  quantity  of  heat  expended  in  heating  and  vaporizing  the  water  to  the 
quantity  of  heat  representing  the  calorific  power  of  the  fuel  consumed. 

The  quantity  of  heat  usefully  expended  in  raising  the  temperature  and  vaporizing 
the  water  is  the  difference  between  the  quantity  of  heat  generated  in  the  furnace  and 
the  quantity  of  heat  present  in  the  gases  discharged  from  the  chimney,  less  the  quan- 
tity of  heat  lost  by  external  radiation  and  conduction. 

The  efficiency  of  the  furnace  determines  the  total  quantity  of  heat  generated,  and 
the  weight  and  temperature  of  the  products  of  combustion.  (See  section  13,  chap- 
tern.) 

The  efficiency  of  the  heating-surface  determines  the  temperature  of  the  gases  dis- 
charged from  the  chimney.  (See  section  5  of  the  present  chapter.) 

The  loss  of  efficiency  due  to  external  radiation  and  conduction  has  been  discussed 
in  section  6  of  the  present  chapter. 

Ordinarily  from  20  to  33  per  cent,  of  the  total  heat  of  combustion  is  expended  in 
the  production  of  chimney-draught  in  marine  boilers.  The  additional  losses  of  heat  by 
radiation,  by  the  incomplete  combustion  of  the  solid  or  gaseous  parts  of  the  fuel,  and 
by  the  dilution  of  the  gases  of  combustion  with  an  excess  of  air  reduce  the  amount  of 
heat  available  for  heating  the  water  to  about  60  per  cent,  of  the  total  heat  of  combus- 
tion in  average  practice  with  marine  boilers. 


SEC.  7.  TRANSMISSION  OP  HEAT  AND  EVAPORATION.  65 

"  When  the  draught  is  produced  by  means  of  a  blast-pipe  or  of  a  blowing-machine 
no  elevation  of  temperature  above  that  of  the  external  air  is  necessary  in  the  chimney  ; 
therefore  furnaces  in  which  the  draught  is  so  produced  are  capable  of  greater  economy 
than  those  in  which  the  draught  is  produced  by  means  of  a  chimney.  It  appears,  fur- 
ther, that  with  a  forced  draught  there  is  less  air  required  for  dilution,  consequently  a 
higher  temperature  of  the  fire,  consequently  a  more  rapid  conduction  of  heat  through 
the  heating-surface,  consequently  a  better  economy  of  heat  than  there  is  with  a  chim- 
ney-draught." (Rankine.) 

The  following  formula  has  been  devised  by  Rankine  to  express  "  to  an  approxi- 
mate degree  of  accuracy"  the  efficiency  of  a  boiler: 

—  -   Bs    •  nv i 

E  ~S+AF    L  V-J 

E  denotes  the  theoretical  evaporative  power,  and  E1  the  actual  evaporative  power  of 
one  pound  of  a  given  sort  of  fuel  consumed  in  a  boiler ;  B  and  A  are  constants,  which 
are  found  empirically  ;  "the  value  of  A  is  probably  proportional  approximately  to  the 
square  of  the  quantity  of  air  supplied  per  pound  of  fuel"  ;  8  denotes  the  number  of 
square  feet  of  heating-surface  per  square  foot  of  grate,  and  fthe  number  of  pounds  of 
fuel  burned  per  hour  per  square  foot  of  grate. 

"  The  following  are  the  values  of  the  constants  B  and  A  which  have  been  found  to 
agree  best  with  experiment,  so  far  as  the  practical  performance  of  boilers  has  hitherto 
been  compared  with  the  formula : 

Boiler  Class  I.  The  convection  taking  place  in  the  best  manner,  either 
by  introducing  the  water  at  the  coolest  part  of  the  boiler  and 
making  it  travel  gradually  to  the  hottest,  or  by  heating  the  feed- 
water  in  a  set  of  tubes  in  the  uptake  ;  the  draught  produced  by  B  A 

a  chimney, 1          o.5 

Boiler  Class  II.     Ordinary  convection  and  chimney-draught,    ....         ft         0.5 

Boiler  Class  III.  Best  convection  and  forced  draught, 1          0.3 

Boiler  Class  IV.  Ordinary  convection  and  forced  draught,       ....         ££         0.3 

"  When  there  is  a  feed-water  heater  its  surface  should  be  included  in  computing 
£"  .  .  .  "  The  formula  is  framed  on  the  supposition  that  the  admission  of  air  and  the 
management  of  fire  are  such  that  no  appreciable  loss  occurs,  either  from  imperfect  com- 
bustion or  from  excess  of  air,  the  construction  and  proportions  of  the  furnace,  and  the 
mode  of  using  it,  being  the  best  possible  for  each  kind  of  coal."  (Rankine.} 


STEAM  BOILERS. 


CHAP.  III. 


8.  Influence  of  the  Rate  of  Combustion  on  the  Evaporative  Efficiency  of 
Boilers  (Isherwood,  '  Experimental  Researches ,'  vol.  ii.) — "  The  economic  and  poten- 
tial evaporations  of  boilers,  other  things  equal,  are  greatly  affected  by  the  rate  of  combus- 
tion. With  each  increase  in  that  rate  above  about  5  pounds  of  combustible  per  square 
foot  of  grate  per  hour,  the  economic  evaporation  decreases  and  the  potential  evaporation 
increases."  .  .  .  "In  the  following  table  will  be  found  (for  the  horizontal  fire-tube 

TABLE  VII. 

SHOWING  THE  ECONOMICAL   AND    POTENTIAL   EVAPORATION  OF  THE  HORIZONTAL  FIRE-TUBE 
BOILER  WITH  ANTHRACITE  CONSUMED  WITH   DIFFERENT  RATES  OF  COMBUSTION. 


Pounds  of 
anthracite  con- 
sumed per  hour 
per  square  foot 
of  grate-surface. 

Pounds  of 
water  evaporat- 
ed under  atmo- 
spheric pressure 
from  212°  Fahr. 
by  one  pound  of 
anthracite. 

Per  centum  of 
the  total    heat 
developed   by 
the  combustion, 
utilized  evapo- 
rative ly. 

Temperature 
in  degrees  Fahr. 
of  the  products 
of    combustion 
when  leaving 
the  boiler. 

Weights  of 
steam  furnished 
by  the  boiler  in 
equal  time, 
expressed    pro- 
portionally. 

Weights  of 
steam  furnished 
by  equal 
weights  of 
anthracite,  ex- 
pressed   propor- 
tionally. 

Weights  and 
bulks  of  anthra- 
cite required  to 
furnish  equal 
weights  of 
steam,  express- 
ed proportion- 
ally. 

6 

10.49 

84.42 

444-7 

.OOOO 

I.  OOOO 

I.  OOOO 

7 

10.44 

84.01 

454-8 

.l6ll 

0.9952 

1.0048 

8 

io-3S 

83-59 

472.6 

•'3124 

0.9867 

I.OI35 

9 

10.23 

82.33 

496-3 

.4628 

0.9752 

1.0254 

10 

10.05 

80.88 

532.o 

.5967 

0.9580 

1.0438 

ii 

9.81 

78-95 

5796 

•7M5 

0.9352 

1.0693 

12 

9-53 

76.69 

635-5 

.8169 

0.9085 

I.IOO7 

13 

9.21 

74.12 

699.0 

1.9023 

0.8780 

1.1389 

14 

8.87 

71.38 

766.6 

1.9730 

0.8456 

I.I826 

15 

8.52 

68.56 

836.3 

2.0305 

O.8I22 

I.23I2 

16 

8.21 

66.07 

897.7 

2.0871 

0.7826 

1.2778 

17 

7-95 

63.98 

949-3 

2-1473 

0-7579 

1.3I94 

18 

7.70 

61.97 

999.0 

2.2021 

0.7340 

1.3624 

*9 

7.48 

60.19 

1042.9 

2.2580 

0.7131 

1.4023 

20 

7-32 

58-91 

i°74-5 

2.3260 

0.6978 

I-433I 

21 

7.16 

57.62 

1  106.4 

2.3890 

0.6825 

1.4652 

22 

7.04 

56-65 

"30.3 

2.4608 

0.67II 

I.490I 

23 

6.92 

55-69 

1154.0 

2.5288 

0.6597 

I-5I58 

24 

6.82 

54.88 

1174.0 

2.6oo6 

0.6501 

I-5382 

boiler,  with  the  tubes  above  the  furnace)  the  principal  results  due  to  different  rates  of 
combustion,  varying  from  6  to  24  pounds  of  anthracite  per  square  foot  of  .grate-surface 
per  hour,  supposing  its  refuse  to  be  one-sixth."  .  .  .  "The  calorimeter  is  taken  at 
one-eighth  of  the  grate-surface,  and  the  heating-surface  at  25  times  the  grate-surface. 
The  economic  evaporation  is  given  in  pounds  of  water  evaporated  under  atmospheric 
pressure  from  212°  Fahr.  per  pound  of  anthracite.  The  economic  evaporation  is  also 


SEC.  9.  TRANSMISSION  OP  HEAT  AND  EVAPORATION.  67 

expressed  in  '  Per  centum  of  the  Total  Heat  developed  by  the  Combustion,  utilized 
evaporatively.'  This  is  calculated  on  the  supposition  that  the  theoretical  economic 
evaporation  of  the  pound  of  anthracite  with  one-sixth  of  refuse  is  12.4263  pounds  of 
water  under  atmospheric  pressure  from  212°  Fahr.  .  .  .  From  these  per  centum — and 
assuming  the  temperature  of  the  products  of  combustion  in  the  furnace,  at  the  moment 
of  their  formation,  to  be  2,469°  Fahr.  above  that  of  the  atmosphere  (taken  at  60°  Fahr.), 
due  to  an  air-supply  of  twice  that  which  is  chemically  necessary  for  perfect  combustion 
—the  temperature  of  the  products  of  combustion,  when  leaving  the  boiler,  is  easily  cal- 
culated." ..."  The  quantities  in  the  second  column  of  the  table — namely,  the 
poiinds  of  water  evaporated  under  atmospheric  pressure  from  212°  Fahr.  by  one  pound 
of  combustible — are  the  means  given  by  a  careful  collation  of  the  results  of  all  the  expe- 
riments with  the  respective  boilers." 

9.  Superheated.  Steam. — When  the  saturated  steam  generated  in  a  boiler  is 
brought  into  contact  with  heating-surfaces  the  absorbed  heat  will,  in  the  first  place, 
vaporize  the  particles  of  water  held  in  suspension  in  the  mass  of  steam,  or,  in  other 
words,  dry  the  steam  ;  and  any  additional  heat  absorbed  by  the  dry  steam  will  raise  its 
temperature  above  the  boiling-point  corresponding  to  its  pressure,  or,  in  other  words, 
superheat  the  steam. 

The  experiments  made  by  Tate  and  Fairbairn  on  the  density  of  superheated  steam 
showed  "that,  for  temperatures  within  about  10°  Fahr.  of  the  saturation-point,  the  rate 
of  expansion  [of  superheated  steam]  very  greatly  exceeds  that  of  air  ;  whereas  at  higher 
temperatures  the  rate  of  expansion  very  nearly  approaches  that  of  air.  Hence  it  would 
appear  that  for  some  degrees  above  the  saturation-point  the  steam  is  not  decidedly  in 
an  aeriform  state,  or,  in  other  words,  that  it  is  watery,  containing  floating  vesicles  of 
un vaporized  water." 

By  drying  and  superheating  steam  its  dynamic  efficiency  in  the  engine  is  increased, 
and  fuel  is  economized  in  consequence.  Comparing  the  efficiency  of  superheated  steam 
with  that  of  dry  saturated  steam,  Rankine  calculates  that,  in  an  engine  using  steam  of 
an  initial  pressure  of  34  pounds  on  the  square  inch  and  expanding  it  to  five  times  its 
original  volume,  by  superheating  the  steam  so  as  to  raise  its  temperature  from  257°.  5  to 
428°  a  saving  of  about  15  per  cent,  would  be  effected ;  and,  in  case  the  whole  of  the 
superheating  is  effected  by  heat  which  would  otherwise  have  been  wasted,  the  saving 
would  be  about  23  per  cent.  In  practice  a  still  greater  saving  has  frequently  been 
effected  by  the  introduction  of  superheaters,  even  when  a  more  moderate  degree  of 
superheating  was  employed — probably  in  consequence  of  the  additional  increase  in  effi- 
ciency due  to  drying  the  steam. 


68  STEAM  BOILERS.  CHAP.  HI. 

The  following  are  some  of  the  results  of  Isherwood's  experiments  with  superheated 
steam  recorded  in  '  Experimental  Researches,'  vol.  ii. : 

In  the  U.  S.  S.  Mackinaw  the  superheating  was  effected  by  carrying  the  water-level 
from  4  to  6  inches  below  the  upper  tube-plate  in  the  "Martin"  boiler.  When  the 
steam  was  cut  off  at  0.70  and  0.21  of  the  stroke  of  the  piston  from  the  commencement, 
the  gain  by  superheating  was  34.02  per  centum  and  38.85  per  centum  of  the  cost  with 
saturated  steam,  respectively. 

In  the  U.  S.  S.  Eutaw  the  superheating  apparatus  described  in  section  3,  chapter 
xii.,  was  used.  With  an  expansion  due  to  cutting  off  the  steam  at  0.32  of  the  stroke  of 
the  piston  from  the  commencement  the  cost  of  the  indicated  horse-power  was  8.67  per 
centum  less  with  steam  superheated  79°.7  Fahr.  than  with  saturated  steam.  With  an 
expansion  due  to  cutting  off  the  steam  at  0.58  of  the  stroke  of  the  piston  from  the  com- 
mencement the  cost  of  the  indicated  horse-power  was  14.76  per  centum  less  with  steam 
superheated  123°.2  Fahr.  than  with  saturated  steam. 

In  the  steamer  Qeorgeanna  the  superheating  was  effected  partly  in  the  steam-drum 
surrounding  the  uptake,  and  partly  in  a  system  of  pipes  within  the  uptake.  The  steam- 
superheating  surface  in  the  steam-drum  alone,  amounting  to  299  square  feet,  was  suffi- 
cient to  impart  enough  additional  heat  to  the  steam  not  only  to  prevent  all  condensa- 
tion of  it  in  the  cylinder  due  to  any  cause  whatever,  but  to  enable  it  to  reach  the  end 
of  the  stroke  of  the  piston  in  a  superheated  state  ;  and  this  amount  of  superheating  in- 
creased the  economic  efficiency  of  the  steam  two-eighths  above  that  due  to  it  as  satu- 
rated steam. 

The  superheating-pipes  and  the  steam-drum  combined,  containing  an  aggregate 
heating-surface  of  900  square  feet,  raised  the  temperature  of  the  steam  as  it  entered  the 
cylinder  to  335°  Fahr.,  while  its  pressure  varied  between  20  and  30  pounds  per  square 
inch  above  the  atmosphere  ;  and  the  economic  efficiency  of  the  steam  was  increased 
thereby  three-eighths  above  that  due  to  it  as  saturated  steam. 

"  The  greater  the  degree  of  superheating  the  greater  will  be  the  gain,  but  not  pro 
rata.  .  .  .  The  benefits  derived  from  superheating,  for  a  given  number  of  degrees, 
are  much  greater  at  the  commencement  of  the  superheating  than  at  the  end,  because  the 
rate  of  expansion  is  higher  near  the  saturation-point,  because  the  prevention  of  conden- 
sation in  the  cylinder  is  completed  with  a  very  moderate  amount  of  superheating,  and 
because  the  loss  from  radiation  is  less.  Practically,  too,  more  steam  is  lost  by  leakage, 
with  the  same  pressure,  past  the  cylinder-piston  and  valves  the  more  it  is  rarefied  by  the 
superheating ;  and  after  a  certain  temperature  is  reached  the  friction  of  the  piston 
is  materially  increased  by  additional  increments,  and  by  tighter  packing  rendered 


SBC.  10.  TRANSMISSION  OF  HEAT  AND  EVAPORATION.  69 

necessary  to  prevent  excessive  leakage."      (Isherwood,   '  Experimental  Researches,'1 

vol.  ii.) 

On  account  of  these  practical  difficulties  it  is  not  considered  advisable  to  let  the  tem- 
perature of  superheated  steam  exceed  greatly  300°  Fahr.  When  the  temperature  of 
saturated  steam  exceeds  that  point  it  is  better  to  add  only  enough  heat  to  the  steam 
after  it  is  generated  to  dry  it,  and  to  prevent  condensation  in  the  cylinders  by  steam- 
jackets. 

1O.  Efficiency  of  Superheating-surfaces. — The  term  "  superheating-surface" 
is  applied  to  all  heating-surfaces  passing  through  the  steam-room  of  a  boiler. 

According  to  section  5  of  the  present  chapter  a  superheating  apparatus  would  be 
most  efficient — that  is  to  say,  transmit  the  greatest  proportion  of  the  total  available  heat 
per  unit  of  surface — if  placed  at  the  hottest  part  of  the  furnace.  The  superheating 
apparatus  is,  however,  usually  placed  in  the  uptake  of  the  boiler,  where  it  absorbs  a 
portion  of  the  heat  of  the  escaping  gases.  In  some  cases  special  furnaces  have  been 
used  for  superheating  the  steam. 

Two  methods  of  superheating  steam  in  boilers  may  be  distinguished — viz.,  either  all 
the  steam  which  is  generated  passes  through  the  superheating  apparatus  placed  be- 
tween the  boilers  and  the  engines,  or  only  a  portion  of  the  steam  which  is  generated 
enters  the  superheater,  and  is  mixed  in  greater  or  less  proportions  with  the  saturated 
steam  coming  directly  from  the  boilers  before  it  passes  to  the  engines.  The  latter 
method  was  introduced  by  Wethered,  and  the  degree  of  superheating  can  be  regulated 
by  it  to  a  great  nicety. 

In  calculating  the  gain  in  the  efficiency  of  a  boiler  by  the  addition  of  superheating- 
surface  the  heat  absorbed  in  drying  the  steam  has  to  be  regarded  as  expended  in  evapo- 
rating an  additional  amount  of  water.  The  addition  of  superheating-surface  in  the 
uptake  frequently  increases  the  economic  evaporative  efficiency  of  the  boiler  at  the  ex- 
pense of  its  potential  evaporative  efficiency  (because  the  chimney-temperature  is  low- 
ered, and  the  additional  heating-surface  offers  an  additional  amount  of  resistance  to 
the  escaping  gases),  unless  without  the  superheating-surface  the  temperature  would  ex- 
ceed the  limit  given  in  section  11,  chapter  ii. 

Isherwood  found  that  by  properly  proportioned  water-heating  surfaces  the  evapora- 
tion in  the  boilers  of  the  Georgeanna  (see  section  9  of  the  present  chapter)  could  have 
been  16.5  per  centum  greater  for  the  same  amount  of  coal.  "Now,  we  have  seen  the 
gain  by  superheating  in  the  case  of  the  Georgeanna  to  be  three-eighths  of  the  effect  of 
saturated  steam  from  her  boiler ;  consequently  we  find  that  it  is  more  economical  to  ex- 
pend heat  in  superheating  steam  after  it  is  generated  than  in  generating  its  equivalent 


70  .  STEAM  BOILERS.  CHAP.  III. 

of  saturated  steam,  by  (37.5  — 16.5)  =  21  per  centum.  It  is  therefore  advantageous,  by 
this  amount,  to  provide  a  separate  superheating  apparatus,  and  superheat  the  steam  in 
it  by  the  direct  expenditure  of  fuel,  in  those  cases  in  which  it  is  not  allowable  to  place 
the  superheater  in  the  uptake  on  account  of  the  height  required — very  objectionable  in 
war-steamers — taking  care  at  the  same  time  to  employ  a  type  and  proportion  of  boiler 
that  will  give  the  maximum  evaporation."  (IsTierwood,  ''Experimental  ResearctiesJ 
vol.  ii.) 

Practically  considered,  the  value  of  superheaters  depends,  as  far  as  the  boilers  are 
concerned,  not  only  on  the  economic  and  potential  evaporative  efficiency  of  the  latter, 
but  on  the  additional  bulk,  weight,  and  cost  of  the  superheating  apparatus,  on  the 
labor  and  expense  of  keeping  it  in  working  order,  and  on  its  liability  to  derangement. 


SEC.  10. 


TRANSMISSION  OF  HEAT  AND  EVAPORATION. 


71 


TABLE  VIII. 

SHOWING  PROPERTIES  OF  WATER  AND  OF  STEAM. 
{From  Isherwootfs  '  Experimental  Researches]  vol.  «'.) 


Total  pres- 
sure of 
steam  in  !bs. 
per  sq.  inch. 

Temperature  in 
degrees  Fahren- 
heit. 
7°. 

Total  units  of 
heat  per  pound 
of  water  from 
32°  to  T°  Fah- 
renheit. 

Total  units  of 
heat  per  pound 
of  steam  from 
32°  to  T  Fah- 
renheit. 

Latent  units  of 
heat  per  pound 
of  steam. 

Weight  of  steam 
per  cubic  foot  in 
fractions  of  a 
pound. 

Cubic  feet  of 
steam  per 
pound. 

Volume  of 
steam,  water  at 
39°.  i  being 
unity. 

I 

101.36 

69-4305 

1112.8548 

1043.4243 

.0034692 

288.2475 

17983.200 

5 

162.51 

130.8914 

1131.5055      IOO0.6l4I 

.0136650 

73.1806 

4565.597 

10 

193.20 

161.8704 

II4O.8660        978.9956 

.0262900 

38.0373 

2373.075 

1469 

2I2.0O 

180.9000 

1146.6000 

965.7000 

.0380071 

26.3109 

1641.424 

15 

213.04 

181.9540 

1146.9172 

964.9633 

•0387839 

25-7839 

1608.607 

20 

227.95 

197.0789 

1151.4647 

954-3858 

.0511491 

I9-5507 

1219.729 

25 

240.07 

209.3952 

n55-l6i3 

945.7661 

.0633879 

15.7760 

984.236 

3° 

250.26 

219.7656 

1158.2693 

938.5037 

•0755004 

13-245° 

826.327 

35 

259.22 

228.8964 

1161.0021 

932.1057 

.0874913 

11.4298 

713.084 

40 

267.17 

237.0076 

1163.4268 

926.4192 

•0993593 

10.0645 

627.903 

45 

274-33 

244.3208 

1165.6106 

921.2898 

.1111084 

9.0002 

561.506 

5° 

280.89 

251.0279 

1167.6114 

916.5835 

.1227283 

8-1473 

508.292 

55 

286.96 

257.2400 

1169.4628 

912.2228 

.1342847 

7-4469 

464.695 

60 

292.58 

262.9967 

1171.1769 

908.1802 

.1456581 

6.8654 

428.319 

65 

297.84 

268.3892 

1172.7812 

904.3920 

•1569473 

6.3716 

397  510 

70 

302.77 

273-4473 

1174.2848 

900.8375 

.1681290 

5-9479 

371.076 

75 

307-42 

278.2219 

'I75-7946 

897-5727 

.1791958 

5-58o5 

348.156 

80 

311.86 

282.7841 

H77-0573 

894.2732 

.1901576 

5-2588 

328.086 

85 

316.08 

287.1234 

1178.3444 

891.2210 

.2OIOII2 

4.9748 

310.368 

90 

320.10 

291.2597 

II79-5705 

888.3108 

.2118493 

4.7222 

294.610 

95 

32394 

295-2I34 

1180.7417 

885.5283 

.2224IO7 

4.4961 

280.506 

100 

327-63 

299.0150 

1181.8671 

882.8521 

•2329599 

4.2926 

267.806 

I05 

33I-I8 

302.6750 

1182.9499 

880.2748 

.2434062 

4.1084 

256-313 

no 

334-59 

306.1920 

1183.9899 

877.7979 

•2537549 

3.9408  i      245.860 

"5 

337-89 

309-5979 

1184.9964 

875-3985 

.2640060 

3.7878  '      236.313 

I2O 

341.06 

312.8713 

"85.9633 

873.0920 

.2742161 

36475 

2.27.560 

I25 

344-13 

3i6-o433 

1186.8996 

870.8563 

.2842203          3-5l84 

219.506 

130 

347-" 

319.1238 

1187.8085 

868.6847 

.2941889          3-3992 

212.068 

T35 

35°-°2 

322.1355 

1188.6961 

866.5606 

.3040635 

3.2881 

205.181 

CHAPTER  IV. 

MATERIALS. 

1.  Relative  Value  of  Materials  for  Boiler-construction. — In  selecting  mate- 
rials for  boiler-construction  it  is  necessary  to  consider  their  strength  under  different  con- 
ditions of  stress,  form,  and  temperature  ;  their  adaptability  for  being  manufactured  into 
the  required  forms  ;  their  behavior  when  exposed  to  heat,  their  cost,  their  durability, 
and  their  weight. 

I.  Regarding  the  strength  of  materials,  it  is  not  sufficient  to  consider  the  tensile  or 
compressive  strain  which  a  small  bar  or  block  of  regular  section  can  bear  in  the  testing- 
machine  ;  in  boilers  the  materials  are  chiefly  employed  in  the  form  of  thin  plates,  pre- 
senting either  flat  surfaces  of  great  extent  or  curves  and  angles  of  every  form,  and  from 
the  manner  of  their  connection  and  the  conditions  obtaining  in  the  use  of  boilers  they 
are  exposed  to  a  great  variety  of  irregular  strains.     The  vast  amount  of  potential  energy 
stored  up  in  the  steam  and  heated  water  of  a  boiler  demands  the  employment  of  a  mate- 
rial possessing  a  high  degree  of  toughness,  in  order  to  mitigate  the  disastrous  conse- 
quences of  a  rupture  ;  for,  while  a  tough  material  simply  tears,  brittleness  would  allow 
large  pieces  to  be  detached  and  hurled  with  great  violence. 

In  this  connection  it  must  be  observed  that  most  metals,  like  copper,  wrought-iron, 
and  steel,  possessing  a  high  degree  of  toughness,  may  become  brittle  by  drawing,  roll- 
ing, and  hammering,  in  consequence  of  a  structural  change  undergone  during  such  pro- 
cess ;  the  original  toughness  can  be  restored,  however,  by  annealing.  "The  strains 
produced  by  unequal  expansion,  in  consequence  of  the  great  difference  of  temperature 
existing  at  different  parts  of  the  boiler,  require  special  attention. 

II.  The  fitness  of  different  materials  for  casting,  rolling,  and  welding,  as  well  as  their 
behavior  when  subjected  to  reheating  for  bending,  to  punching,  drilling,  and  riveting, 
require  consideration.     It  is  very  important  that  the  material  should  be  of  a  reliable 
character,  sound  throughout,  and  of  uniform  strength. 

III.  The  thermal  conductivity  of  different  materials,  as  well  as  their  strength  at  the 
temperatures  obtaining  in  steam  boilers,  varies  greatly. 

72 


SEC.  2. 


MATERIALS.  73 


IV.  The  cost  of  materials  is  not  measured  merely  by  the  market  price  of  the  raw 
pigs  or  ingots,  sheets,  and  bars,  but  it  is  enhanced,  for  different  materials  in  a  widely 
different  degree,   by  the  difficulties  encountered  during  the  processes  which  convert 
them  into  constituent  parts  of  a  boiler.     The  final  cost  of  a  boiler  is  modified  consider- 
ably by  its  durability  as  well  as  by  the  value  of  the  old  material. 

V.  Durability,  the  power  of  resisting  the  destructive  effects  of  the  various  stresses 
and  chemical  agencies  to  which  boilers  are  exposed,  is  of  importance  not  only  in  so  far 
as  it  affects  their  cost  but  also  their  efficiency  ;  especially  in  the  boilers  of  war-vessels 
that  have  to  maintain  their  efficiency  while  engaged,  for  many  months  continuously,  on 
distant  stations  without  adequate  facilities  for  repairs. 

VI.  The  problem  of  producing  the  maximum  effect  with  the  minimum  weight  of 
material  is  of  increasing  importance  in  modern  marine  engineering,  especially  for  war- 
vessels. 

There  is  no  substance  that  will  pre-eminently  satisfy  all  the  foregoing  requirements, 
and  the  selection  of  the  proper  material  for  different  parts  of  a  boiler  has  to  be  governed 
by  experience  as  to  their  special  fitness,  and  by  the  exercise  of  judgment  as  to  the  rela- 
tive value  of  their  properties  in  each  case.  Since  wrought-iron  has  been  for  many  years 
the  principal  material  employed  in  boiler-construction,  it  is  convenient  to  use  it  as  a 
standard  for  measuring  the  relative  fitness  of  other  metals  for  this  purpose. 

2.  Copper. — Copper  was  largely  used  for  the  shell  of  boilers  when  steam  of  compa- 
ratively low  pressure  was  employed.  Wilson  says  that  the  advantages  possessed  by 
copper  for  boiler-making  consist  "in  the  uniformity  and  homogeneity  of  its  texture,  in 
its  freedom  from  lamination  and  blisters,  and  in  its  general  trustworthy  character  when 
well  selected  ;  in  the  manner  in  which  it  resists  the  tenacious  adhesion  of  most  kinds  of 
incrustation ;  in  its  great  ductility  and  malleability,  which  render  it  capable  of  being 
worked  with  great  ease  and  of  bearing  sudden  as  well  as  oft-repeated  racking  strains  ; 
in  its  being  a  better  conductor  of  heat,  which  not  only  tends  to  give  it  a  higher  evapora- 
tive power  under  favorable  conditions,  but  also  enables  it  to  last  longer  when  exposed 
to  a  fierce  wasting  heat  in  a  boiler-furnace."  An  explosion  generally  results  in  a  simple 
tearing,  and  not  in  a  violent  projection  of  fragments ;  small  leaks  are  easily  calked ; 
finally,  as  old  material,  copper  is  worth  about  two-thirds  as  much  as  when  new. 

On  the  other  hand,  copper  deteriorates  more  rapidly  than  iron  when  coal  containing 
sulphur  or  ammonia  is  burned  in  contact  with  it ;  its  strength  is  inferior  to  that  of  iron 
nearly  in  the  proportion  of  three  to  five  at  ordinary  temperatures,  but  decreases  rapidly 
with  each  increase  of  temperature.  Experiments  made  by  a  committee  of  the  Franklin 
Institute  in  1837  developed  the  fact  that  at  a  temperature  of  550°  it  loses  one-fourth 


74  STEAM  BOILERS.  CHAP.  IV. 

of  its  tenacity  at  ordinary  temperatures,  at  817°  precisely  one-half,  and  at  1,000°  two- 
thirds  of  its  strength  are  destroyed.  Its  first  cost  is  very  high,  being  nearly  five  times 
that  of  iron.  (See  also  chapter  i.) 

At  present  the  use  of  copper  in  boilers  is  almost  entirely  limited  to  the  crown-sheets 
of  English  locomotives,  and,  in  marine  boilers,  to  superheating-tubes,  to  feed,  steam, 
blow,  and  escape  pipes,  and  similar  appendages. 

3.  Composition. — Composition  is  a  general  term  for  certain  alloys  of  copper  and 
tin  or  zinc,  mixed  in  various  proportions  ;  they  are  harder  and  generally  more  tenacious 
than  copper,  and  less  subject  to  oxidation ;  they  are  more  fusible  than  copper,  make 
better  castings,  and  are  more  easily  worked  with  cutting  tools,  while  at  the  same  time 
their  cost  is  less. 

Brass  is  an  alloy  of  copper  and  zinc.  The  quantity  of  copper  varies  from  60  to  92 
per  cent.  ;  the  best  proportion  for  fine  yellow  brass  appears  to  be,  copper  two  parts  and 
zinc  one  part.  The  addition  of  a  little  lead — from  f  to  3  per  cent. — causes  the  brass  to 
be  more  ductile  and  better  adapted  for  turning  in  a  lathe,  but  reduces  the  tenacity  of 
the  metal ;  a  larger  addition  of  lead  renders  the  metal  brittle.  Instead  of  lead  tin  is 
sometimes  added,  which  renders  the  metal  more  homogeneous  and  increases  its  fluidity 
without  impairing  its  tenacity.  Brass  is  more  malleable  than  copper  when  cold,  but 
cannot  be  forged  at  a  red  heat,  on  account  of  the  low  melting-point  of  zinc.  It  is  very 
extensively  used  for  castings  and  for  brazed  and  drawn  pipes  and  tubes. 

Drawn  seamless  boiler-tubes  have  almost  entirely  stiperseded  iron  tubes  in  the  ves- 
sels of  the  United  States  Navy.  Their  thermal  conductivity  is  greater  than  that  of  iron 
in  the  proportion  of  1.4  to  1,  and  their  superior  ductility  makes  it  possible  to  render  their 
joints  tight  without  straining  the  metal  to  an  undue  degree ;  at  the  same  time  brass 
tubes  can  be  made  about  20  per  cent,  thinner  than  iron  ones,  while  their  freedom  from 
corrosion  gives  them  a  reliability  and  durability  which  far  outweigh  their  original  in- 
creased cost  over  that  of  iron. 

Bronze.  Such  parts  of  the  machinery  of  United  States  naval  vessels  as  require  a 
high  degree  of  tenacity  combined  with  freedom  from  corrosion  and  lightness  are  made  of 
a  composition  consisting  of  88  parts  of  copper,  10  parts  of  tin,  and  2  parts  of  zinc. 

By  adding  a  small  portion  of  dry  phosphorus  to  these  alloys  in  the  crucible,  before 
running  them  into  the  mould,  they  are  rendered  so  liquid  that  very  thin  and  sound 
castings  may  be  obtained,  while  at  the  same  time  the  hardness  and  the  tenacity  of  the 
metal  are  considerably  increased. 

Where  expense  is  a  secondary  consideration,  and  where  it  is  specially  desirable  to 
avoid  corrosion  and  lessen  weight,  the  use  of  composition  is  extended  to  val\;e-cham- 


SEC.  4.  MATERIALS.  75 

bers,  pipes,  screw-swivels  for  long  braces  intended  to  be  removable,  hinges  of  connec- 
tion-doors, manhole-plates,  etc.  When  exposed  to  a  temperature  approaching  a  red 
heat  this  metal  loses  all  tenacity  and  crumbles  to  pieces. 

4.  Tenacity  of  Metals  at  various  Temperatures  (abridged  from  an  article  in 
the  Engineer,  Oct.  5,  1877). — The  accompanying  table  gives  the  results  of  a  series  of 
experiments  made  in  Portsmouth  Dockyard  to  ascertain  the  loss  of  strength  and  duc- 
tility in  gun-metal  compositions  when  raised  in  temperature.  The  object  was  to  see 
whether  gun-metal  would  be  more  or  less  suitable  than  cast-iron  for  stop  and  safety 
valve  boxes,  steam-pipe  connections,  fastenings,  etc.,  etc.,  which  might  be  subjected  to 
high  temperatures,  either  from  superheated  steam  or  proximity  to  hot  uptakes  or  fun- 
nels. The  result  shows  that  it  is  desirable  to  make  further  investigations.  The  speci- 
mens and  dies  for  griping  them  were  heated  in  an  oil  bath,  and  the  temperatures 
recorded  are  those  of  the  oil.  In  the  case  of  gun-metal  three  or  more  tests  were  made 
at  each  temperature,  the  table  giving  the  mean,  except  when  there  were  defects  in  the 
metal.  All  the  composition  specimens  were  run  in  a  horizontal  position  with  a  head  of 
2£  inches,  excepting  those  in  columns  1  and  2.  Those  in  No.  2  were  stronger  at  atmos- 
pheric temperature  than  No.  1,  and  they  suffered  sooner  by  increases  of  temperature. 
All  the  varieties  of  gun-metal  suffer  gradual  but  not  serious  loss  of  strength  and  duc- 
tility up  to  a  certain  temperature,  at  which,  within  a  few  degrees,  a  great  change  takes 
place  ;  the  strength  falls  to  about  one-half,  and  the  ductility  is  wholly  gone.  Above 
this  point,  up  to  500°,  there  is  little  if  any  further  loss  of  strength.  The  precise  tem- 
perature at  which  the  change  and  loss  of  strength  take  place,  although  uniform  in  the 
specimens  cast  from  the  same  pot,  varies  about  100°  in  the  same  composition  at  different 
temperatures  or  with  some  varying  conditions  in  the  foundry  process.  In  No.  1  series 
this  temperature  was  about  370°,  and  in  No.  2  a  little  over  250°.  The  cause  is  not 
known,  but  the  fact  is  certain  and  important.  Phosphor-bronze,  the  only  metal  in  the 
series  which,  from  its  strength  and  hardness,  could  be  used  as  a  substitute,  was  less 
affected  by  temperature,  and  at  500°  retains  more  than  two-thirds  of  its  strength  and 
one-third  its  ductility  ;  but  the  difference  arising  from  variations  in  the  process  of  cast- 
ing or  quality  of  material  used  should  be  tested,  also  whether  the  other  compositions 
may  be  hardened  without  loss  of  strength.  Eolled  Muntz  metal  and  copper  are  satis- 
factory up  to  500°,  and  may  safely  be  used  as  securing-bolts.  Wrought-irons  increase 
in  strength  up  to  500°,  but  lose  slightly  in  ductility  up  to  300°,  where  an  increase  begins 
and  continues  up  to  500°,  where  it  is  still  less  than  at  the  ordinary  temperature  of  the 
atmosphere.  The  strength  of  Landore  steel  is  not  affected  by  temperature  up  to  500°, 
but  its  ductility  is  reduced  more  than  one-half. 


76 


STEAM  BOILERS. 


CHAP.  IV. 


8 

10 

O 
H 


Bi 

M 
P. 


ti  S 


s  ^ 

hJ  W 

M  « 

<  s 

EH  b 


S 


O 

•2 


Jl 


S-j-Jf 

^a^ ' 


1 


ii! 

£    R 


1J 


Ss^j 


jlj 


4    4  i 


•  f 


f  • 


111 


e     |         $    »    S, 

If!  11? 


1   4 


«  ; 


*****;& 


3 
I 


.    8 

O      --       J3 

U     H     fu 


•••MMllllliit 


'XjlJIJOtlQ 


I      « 


*S 


0& 


u    P 


h 


'g     if    S    »    « 


S  S  S  4 


•Xjt|tjonci 


Bi  . 


8s    ff     i 


if    R  j    _• 

a'   s   s   s   s   s  •*    '  '2  '= 


4         8  °&  8  °a  a 

fe     rt  a    M|-|"M« 


I 

i 


I 

•3 


I 


.S  8 

S-g 


•3  » 

rt    C 


SKC.  5.  MATERIALS.  77 

5.  Cast-iron. — Cast-iron  is  used  for  grate-bars,  ashpans,  furnace  and  uptake  doors, 
manhole  and  handhole  plates,  valve-chambers,  steam,  feed,  blow,  and  dry  pipes,  and 
other  boiler  appendages.     Its  low  first  cost  and  the  ease  with  which  it  can  be  worked 
give  it  great  advantages  for  such  purposes  ;  but  the  uncertainty  of  strength  caused  by 
defective  moulding,  its  brittleness  and  low  tensile  strength,  render  it  unfit  for  extensive 
use  for  parts  of  the  boiler  proper.     Its  unyielding  nature  unfits  it  specially  for  parts 
subjected  to  unequal  expansion  from  differences  of   temperature.     Several  kinds  of 
modern  sectional  boilers  consist,  however,  almost  entirely  of  small  cast-iron  spheres  or 
tubes. 

6.  Wrought-iron. — Wrought-iron  has  been  for  many  years  the  material  most  ex- 
tensively used  in  boiler-making.     Wilson  sums  Tip  the  advantages  possessed  by  it  for 
this  purpose  in  the  following  words  :  "The  great  tensile  strength  of  good  wrought-iron, 
together  with  its  ductility,  power  of  bearing  sudden  and  trying  strains,  and  general 
trustworthy  nature,  its  moderate  facilities  for  working,  the  ease  with  which  it  can  be 
welded,  riveted,  patched,  or  mended,  its  moderate  first  cost  compared  with  copper,  are 
all  important  advantages  which  contribute  to  its  value." 

It  enters  into  the  construction  of  boilers  as  plates,  varying  from  \"  to  1 J*  in  thickness, 
as  rivets,  round  bar-iron  and  flat  iron,  J  and  angle  iron,  and  drawn  seamless  and  lap- 
welded  tubes.  In  order  to  reduce  the  weight  of  boilers  as  much  as  possible  wrought- 
iron  is  frequently  used  instead  of  cast-iron  for  furnace,  ashpit,  and  uptake  doors,  for 
ashpans,  manhole-covers,  and  sometimes  for  grate-bars. 

The  wrought-iron  used  in  the  construction  of  the  boiler  proper  should  be  of  the  best 
quality;  it  must  possess  not  only  great  tensile  strength  but  a  high  degree  of  duc- 
tility, and  it  must  bear,  without  receiving  serious  injury,  the  severe  treatment  to  which 
it  is  subjected  by  repeated  heating,  welding,  hammering,  punching,  and  drilling.  The 
quality  of  wrought-iron  depends  upon  the  chemical  composition  of  the  cast-iron  or  the 
ore  from  which  it  has  been  made,  and  of  the  fuel  used  during  the  process  of  conver- 
sion ;  on  the  thoroughness  with  which  the  slag,  cinders,  and  other  deleterious  sub- 
stances have  been  removed  ;  and  on  the  general  care  and  labor  expended  on  it  during 
the  processes  of  refining,  squeezing,  hammering,  and  rolling.  The  most  common  defect 
of  boiler-plates  arises  from  the  imperfect  welding  of  the  several  layers  of  metal  forming 
the  plate,  owing  to  the  interposition  of  sand  or  cinders ;  the  laminations  and  blisters 
produced  in  this  manner  are  sometimes  difficult  to  detect,  but  will  appear  sooner  or 
later  when  the  plate  is  exposed  to  the  intense  heat  of  the  furnace.  The  presence  of  a 
small  trace  of  sulphur  produces  hot-shortness  in  iron,  which  means  that  it  will  not 
work  advantageously  and  becomes  brittle  when  red-hot,  but  is  strong  and  pliable  when 


78  STEAM  BOILERS.  CHAP.  IV. 

cold.  On  the  other  hand,  the  presence  of  phosphor  and  silicon  produces  cold-short- 
ness, which  means  that  the  iron  will  not  stand  bending,  twisting,  or  punching  near  the 
edges  when  cold.  An  increase  in  the  percentage  of  carbon  renders  the  iron  harder,  less 
ductile,  and  more  difficult  to  weld. 

During  the  process  of  rolling  into  bars  or  plates  iron  assumes  a  fibrous  texture,  and 
boiler-plates,  as  a  rule,  are  stronger  when  the  tension  takes  place  in  the  direction  of  the 
fibre  than  when  it  is  applied  at  right  angles  to  the  fibre.  Increase  of  temperature  does 
not  diminish  the  strength  of  iron  till  it  reaches  about  400°. 

7.  Brands  of  Plate-iron  used  in  Boiler-making. — The  use  of  mineral  fuel  is 
generally  dispensed  with  in  the  manufacture  of  boiler-iron,  and  wood  charcoal  is  em- 
ployed instead,  in  order  to  avoid  the  admixture  of  deleterious  foreign  substances.  Such 
iron  is  designated  by  the  name  of  "charcoal-Iron." 

The  following  are  the  various  brands  of  American  plate-iron  commonly  used  for  ma- 
rine boilers,  arranged  in  the  order  of  their  excellence  and  cost :  Charcoal  No.  1  Iron 
(C.  No.  1)  will  bear  40,000  Ibs.  tensile  strain  in  the  direction  of  the  fibre ;  it  is  pretty 
hard  and  is  never  flanged  ;  it  is  often  used  for  the  interior  parts  of  a  boiler,  but  breaks 
or  furrows  easily  when  exposed  to  bending  strains.  Another  brand  (C.  No.  1  R.  H.\ 
Charcoal  No.  1  Reheated-  Iron,  is  a  very  durable  iron  for  fire-boxes,  since,  on  account 
of  its  hardness,  it  resists  the  oxidizing  influence  of  the  flame  ;  but  it  breaks  easily  under 
alternating  bending  strains. 

Charcoal  Hammered  No.  1  Shell-iron  (C.  H.  No.  I  S.),  though  not  necessarily  ham- 
mered, has  been  worked  more  thoroughly  than  the  previous  brands  before  it  is  rolled 
into  plates.  It  will  bear  in  the  testing-machine  from  50,000  Ibs.  to  54,000  Ibs.  of  tensile 
strain  per  square  inch  in  the  direction  of  the  fibre,  and  from  34,000  to  44,000  Ibs.  across 
the  fibre.  It  is  a  rather  hard  iron  and  cannot  be  flanged  ;  at  least  it  should  not  be  bent 
along  the  fibre,  but  always  across  the  fibre  and  with  a  pretty  large  radius.  It  is  used 
especially  for  the  outside  shell  of  boilers. 

C.  II.  No.  I  F.  (Flange}  Iron  is  a  soft  material,  which  can  be  flanged  in  every  direc- 
tion. It  will  bear  from  50,000  to  54,000  Ibs.  of  tensile  strain  per  square  inch  along  the 
fibre,  and  the  best  qualities  do  not  show  a  much  smaller  strength  when  the  strain  is 
applied  across  the  fibre. 

C.  H.  No.  1  F.  B.  (Fire-box)  Iron  is  a  harder  quality,  designed  to  withstand  the  de- 
structive effect  of  the  impinging  flame  ;  it  will  generally  bear  flanging.  There  is,  how- 
ever, another  quality,  marked  C.  H.  No.  I  F.  F.  B.  (Flange  Fire-box)  Iron,  or  Extra 
Fire-box  or  Excelsior  Fire-box  Iron,  which  is  generally  used  for  flanged  fire-box 
plates. 


SEC.  8.  MATERIALS.  79 

There  are  special  brands,  as  Sligo,  N.  P.  U.  Iron  (made  at  the  Lukens  Rolling-mills, 
Coatesville,  Chester  Co.,  Pa.),  Eureka  (manufactured  by  C.  E.  Pennock  &  Co.,  Valley 
Iron-works,  Coatesville,  Pa.),  and  Pine  Iron,  which  command  high  prices,  and  are 
specially  fitted  to  withstand  the  destructive  effect  of  heat  or  to  be  worked  into  the  most 
difficult  forms. 

These  "  charcoal-irons'1''  are  manufactured  principally  in  Pennsylvania. 

The  greatest  width  of  boiler-plates  made  at  different  establishments  varies  between 
48  inches  and  96  inches,  and  the  extreme  weight  of  the  trimmed  plate  between  1,000 
and  1,800  Ibs.  The  length  of  the  plate  varies  frequently  with  the  width ;  with  some 
manufacturers  it  is  the  rule  to  deduct  one  inch  in  width  for  each  additional  foot  in 
length :  for  instance,  if  the  dimensions  of  the  widest  plates  are  76"  x  76",  narrower 
plates  would  have  the  following  dimensions  :  75"  X  88",  74"  X  100",  73"  x  112",  etc. 

The  best  English  boiler-iron  is  the  Yorkshire  iron,  which  seems  to  owe  its  superi- 
ority partly  to  the  fact  that  the  coal  used  in  the  reduction  of  the  ore  and  the  manufac- 
ture of  the  plates  is  remarkably  free  from  sulphur  and  phosphorus.  Wilson  says: 
"  The  most  prominent  makers  of  boiler-plates  are  the  so-called  '  Best  Yorkshire '  houses 
(viz.,  The  Low  Moor  Iron- works,  near  Bradford  ;  Taylor  Brothers  &  Co.,  Leeds  ;  Bowl- 
ing Iron  Co.,  near  Bradford  ;  Farnley  Iron  Co.,  near  Leeds  ;  S.  T.  Cooper  &  Co.,  Leeds  ; 
and  The  Monk  Bridge  Iron  Co.,  Leeds;  the  other  firms  who  make  only  'Best  York- 
shire '  iron  do  not  roll  plates),  who  only  turn  out  one  class  of  iron,  and  that  the  very 
best,  if  we  except  some  of  the  Swedish  and  Russian  brands." 

8.  Steel.— The  use  of  steel  in  boiler-construction  has  attracted  much  attention  of 
late,  especially  since  the  introduction  of  improved  processes  of  manufacture,  which 
have  resulted  in  the  production  of  much  more  uniform  qualities  of  steel  than  were 
formerly  obtainable,  and  in  a  reduction  of  its  cost  which  allows  it  to  compete  in  many 
cases  with  wrought-iron  in  economical  respects. 

The  steel  used  for  boiler-plates  is  sometimes  crucible  steel,  but  is  generally  manu- 
factured by  the  Bessemer  or  the  Siemens-Martin  process.  It  must  be  of  a  very  mild 
quality,  containing  about  one-quarter  or  one-third  per  cent,  of  carbon.  Steels  contain- 
ing a  larger  amount  of  carbon  possess  greater  tensile  strength,  but  are  brittle,  hard  to 
work,  and  untrustworthy  for  use  in  boiler-making.  It  is  very  important  that  steel 
boiler-plates  do  not  temper  when  suddenly  cooled  down  from  a  red  heat.  Steel  loses 
this  characteristic  of  taking  a  temper  when  the  percentage  of  carbon  is  reduced  below 
a  certain  amount,  while  at  the  same  time  its  welding  qualities  are  improved.  In  fact, 
the  milder  kinds  of  steel  possess  all  the  good  qualities  of  wrought-iron,  only  in  a 
higher  degree,  and  differ  from  it  principally  by  their  greater  purity  and  their  perfectly 


80  STEAM  BOILERS.  CHAP.  IV. 

homogeneous  structure.  While  iron  boiler-plate  is  produced  by  the  piling  of  a  number 
of  slabs,  separately  manufactured  and  undergoing  repeated  reheatings,  steel  plates  are 
rolled  from  single  ingots,  often  at  one  heat.  Each  charge  of  the  hearth  or  converter 
produces  from  five  to  eight  tons  of  metal,  which  can  be  carefully  examined  and  tested, 
and  carburized  or  decarburized  and  refined  to  any  desired  degree,  before  it  is  finally 
drawn  off.  In  this  manner  a  uniformity  in  the  character  of  the  metal  is  produced 
which  is  unattainable  in  the  manufacture  of  iron.  Wilson  says  that,  "in  order  to 
ensure  freedom  from  brittleness,  from  33  to  36  tons  per  square  inch  appears  to  be  the 
maximum  tensile  strength  that  can  be  allowed.  Steel  plates  of  this  strength  can  be 
made  sufficiently  tough  and  ductile  to  render  them  safe  and  also  tolerably  easily 
worked."  But  the  surveyors  to  Lloyd's  Registry  recommend  that  steel  used  in  boiler- 
making  should  have  an  ultimate  tensile  strength  of  not  less  than  26  tons  and  not  more 
than  30  tons  per  square  inch  of  section,  and  the  same  limits  have  been  adopted  by  the 
English  Admiralty. 

Even  the  mildest  steels  seem  to  be  affected  differently  from  iron  by  the  severe  strains 
of  hammering,  punching,  and  shearing ;  to  restore  to  the  plate  its  original  character  it 
is  considered  necessary  to  anneal  it. 

With  regard  to  the  effect  of  corrosion  on  steel  the  opinions  are  much  divided  ;  while 
the  greater  density  and  homogeneity  of  steel  would  lead  one  to  suppose  that  it  would 
suffer  less  than  iron  in  that  respect,  it  is  asserted  that  steel  boilers  have  shown  an  un- 
usual amount  of  corrosion  after  short  use.  This  question  can  only  be  settled  after  fur- 
ther experience  with  the  qualities  of  steel  now  in  use.  In  this  connection  it  must  be 
remembered  that,  since  thin  plates  deteriorate  more  rapidly  relatively  than  thicker 
plates  under  the  influence  of  corrosion,  the  reduction  in  the  thickness  of  steel  boiler- 
plates cannot  be  made  in  the  ratio  of  the  increased  strength  of  steel  over  iron. 

The  following  extracts  are  taken  from  a  report  of  the  surveyors  to  Lloyd's  Registry, 
made  in  the  early  part  of  1878,  which  discusses  the  advantages  and  difficulties  incident 
to  the  use  of  steel  for  boilers  in  a  very  thorough  manner  : 

"The  methods  adopted  in  the  manufacture  of  mild  steel  by  the  Bessemer  and  Sie- 
mens-Martin processes  are  such  as  practically  to  ensure  the  production  of  a  material 
perfectly  reliable  so  far  as  regards  its  uniformity  in  tensile  strength  and  its  power  to 
withstand  certain  bending  tests.  The  limit  of  elasticity  of  this  material  bears  about  the 
same  relation  to  its  ultimate  strength  as  in  ordinary  wrought-iron  ;  but  the  elongation 
or  stretch  under  stresses  proportional  to  the  ultimate  strengths  is  greater  with  steel  than 
with  iron — a  fact  which  should  not  be  lost  sight  of  in  forming  an  estimation  of  the 
strength  of  boilers.  At  first  sight  it  recommends  itself  by  its  tensile  strength,  mallea- 


SEC.  8.  MATERIALS.  81 

bility,  and  ductility,  and  also  by  its  freedom  from  laminations  and  blisters,  as  eminently 
suited  for  the  construction  not  only  of  the  shells  and  stays  but  also  of  the  furnaces  and 
combustion-chambers  of  marine  boilers.  But  while  as  a  material  it  possesses  in  a  special 
degree  these  high  qualities,  it  is  found  that  they  become  seriously  impaired  by  its  being 
subjected  to  the  processes  usually  occurring  in  boiler-making,  and  it  is  necessary  to 
exercise  the  greatest  care  in  the  working  of  it  to  ensure  these  qualities  being  retained  in 
the  structure,  while  in  some  instances  it  is  even  requisite  to  subsequently  employ  spe- 
cial means  in  order  to  restore  them.  The  simple  process  of  shearing  affects  to  some 
extent  the  tensile  strength  of  the  plate  operated  upon,  and  a  considerable  portion  of  its 
strength  is  lost  by  punching.  It  is  contended,  however,  and  indeed  it  may  be  said  to 
be  placed  beyond  doubt,  that  the  loss  thus  occasioned  is  fully  recovered  by  the  plates 
being  annealed  after  they  have  been  sheared  or  punched,  and  it  is  the  practice  at  almost 
all  the  steel  manufactories  we  have  visited  to  anneal  every  plate  after  it  is  sheared  and 
before  being  sent  out  of  the  works.  It  may  be  well  here  to  remark  that  this  annealing 
is  not,  as  is  frequently  supposed,  a  process  of  some  difficulty,  requiring  great  care  and 
considerable  time  in  the  operation.  It  consists  simply  of  heating  the  plates  to  a  low 
red  heat — which  allows  the  particles  that  have  been  strained  or  disturbed  by  the  work- 
ing of  the  material  to  resume  their  normal  condition — and  then  cooling  them  uniformly. 

"At  some  works  the  holes  are  drilled,  and  at  others  punched ;  but  in  all  cases  in 
which  they  are  punched  the  plates  are  afterwards  annealed.  It  is  the  practice  at  all  the 
works,  and  it  is  considered  by  these  firms  to  be  of  the  utmost  importance  to  perform 
the  operation  of  flanging  in  only  one  heat,  if  possible,  and  to  have  the  plates  uniformly 
heated  throughout ;  but  when  this  is  not  practicable,  and  the  operation  is  extended  over 
several  heats — the  plates  being  heated  locally  piece  by  piece,  as  is  usually  done  in  flang- 
ing iron  plates — care  is  taken  that  the  plates  so  flanged  are  afterwards  annealed. 

"The  opinions  of  those  who  maybe  regarded  as  authorities  on  the  matter  differ 
greatly  with  regard  to  the  limits  of  tensile  strength  which  should  be  adopted  for  this 
material  when  intended  for  boiler-making  purposes.  .  .  .  Taking  into  consideration 
the  fact  that  the  milder  material  is  more  easily  worked  and  less  likely  to  be  injured  by 
careless  manipulation  than  that  of  higher  strength  and  more  brittle  nature,  ...  we  are 
of  the  opinion  that  it  would  not  be  prudent,  at  least  until  further  experience  is  gained, 
to  raise  the  limits ;  while  at  the  same  time  it  might  be  advisable  to  recommend  that 
plates  used  in  the  construction  of  the  furnaces  and  combustion-chambers  be  specified  to 
withstand  not  more  than  from  26  to  28  tons  per  square  inch. 

"  With  regard  to  the  question  of  steel  rivets,  it  has  been  conclusively  shown,  by  the 
results  of  some  of  the  experiments  made  on  the  Tyne,  that  they  may  be  used  with  as 


82  STEAM  BOILERS.  CHAP.  IV. 

much  reliability  as  steel  plates,  but  that,  like  the  latter,  they  require  greater  care  and 
discrimination  to  be  exercised  in  the  working  of  them  than  those  made  of  iron.  In  the 
opinion  of  Dr.  Siemens  and  other  authorities  the  material  of  which  the  rivets  are  made 
should  be  very  mild  steel,  the  tensile  strength  not  exceeding  26  tons  per  square  inch. 
It  is  also  needful  to  heat  them  uniformly  throughout  their  entire  length,  and  not  to 
raise  the  points  to  a  higher  temperature  than  the  heads,  as  is  the  usual  practice  with 
iron  rivets,  and  they  should  not  be  heated  beyond  a  bright-red  heat.  When  these  pre- 
cautions are  taken  steel  rivets  will  be  found  to  resist  steady  strains  and  also  jars  and 
concussions  much  better  than  iron  rivets. 

"  In  conclusion,  we  would  remark  that  in  the  construction  of  steel  boilers  greater 
care  and  attention  must  be  exercised  with  the  workmanship  than  is  required  in  the  case 
of  iron  boilers  ;  and  the  difference  between  the  two  materials,  and  the  consequent  diffe- 
rent manipulation  required  in  each  case,  must  be  realized  not  only  by  the  manager,  but 
by  the  workman  who  will  have  to  use  the  material ;  for  if  steel  plates  are  drifted 
heavily  and  knocked  about  as  iron  plates  usually  are  in  boiler-making,  the  material  will 
be  injured.  We  may  expect  to  see  steel  boilers  extensively  used  in  preference  to  those 
made  of  iron,  where  lightness  or  increased  pressure  is  an  object,  while  if  they  are  made 
with  the  care  which  this  material  requires,  and  eventually  prove  to  be  as  durable  as  iron 
boilers,  it  will  be  a  question  whether  a  considerable  reduction  in  the  factor  of  safety 
may  not  be  found  quite  compatible  with  perfect  safety  and  efficiency . 

"After  having  given  all  the  circumstances  in  connection  with  the  whole  matter  our 
most  careful  consideration,  we  would  respectfully  submit  that,  where  it  is  proposed  to 
use  steel  boilers  in  vessels  intended  for  classification  in  this  society's  Register  Book,  the 
requirements  of  the  case  would  be  met  by  sanctioning  a  reduction  from  the  scantlings 
prescribed  by  the  rules  for  iron  boilers,  in  the  shell-plates  and  stays  to  the  extent  of  25 
per  cent.,  and  in  the  flat  plates  not  subject  to  the  action  of  heat  to  the  extent  of  12  per 
cent.,  under  the  following  conditions  : 

"I.  The  material  to  have  an  ultimate  tensile  strength  of  not  less  than  26  tons  nor 
more  than  30  tons  per  square  inch  of  section. 

"II.  A  strip  cut  from  every  plate  used  in  the  construction  of  the  furnaces  and  com- 
bustion-chambers, and  strips  cut  from  other  plates  taken  indiscriminately,  heated  uni- 
formly to  a  low  cherry-red  heat,  and  quenched  in  water  of  82°  Fahr.,  must  stand  bending 
to  a  curve  of  which  the  inner  radius  is  not  greater  than  one  and  one-half  times  the  thick- 
ness of  the  plate  tested. 

"III.  All  holes  to  be  drilled,  or,  if  they  are  punched,  the  plates  to  be  afterwards 
annealed. 


SBC.  8. 


MATERIALS. 


83 


"  IV.  All  plates,  except  those  that  are  in  compression,  that  are  dished  or  flanged,  or 
in  any  way  worked  in  the  fire,  to  be  annealed  after  the  operations  are  completed. 

"  V.  The  boilers  upon  completion  to  be  tested  in  the  presence  of  one  of  the  society's 
engineer-surveyors  to  not  less  than  twice  the  working  pressure." 


TABLE  X. 
EXHIBITING  CERTAIN  PHYSICAL  AND  MECHANICAL  PROPERTIES  OF  VARIOUS  METALS. 


Material. 

Weight  in 
pounds 
per  cubic  foot. 

Expansion  of 
unity  of 
length  from 
32°  to  2  1  2° 
Fahr. 

Ultimate  ten- 
sile strength. 

Elongation  in 
per  cent,  of 

length. 

Shearing 
strength. 

Crushing 
strength. 

\\\  R. 

.001  1  R. 

20  ooo  W 

16,500  H. 

27,700  R. 

112  OOO  R. 

480  R. 

.0012  R. 

Bar-iron   average       ..     .    

481  K. 

en  COO 

50  ooo  R 

38  ooo  R 

51  ooo 

481  K. 

"     in  direction  of  fibre  . 

ec    \'i'i  K 

I'l  A 

"    across  the  fibre  

50,462  K. 

60 

Yorkshire  bar-iron  

484  K. 

61  0";=;  K. 

2J.  J.6 

61  469  K 

2O  46 

*lfi    Tl.l    B 

486  K. 

d.6  7J.7  K 

22  1 

Steel  

490  R. 

.0012  R. 

Landore  steel  boiler-plate  

63  ooo 

2  A  2$ 

Fagersta  steel  boiler-pi.,  unannealed. 
annealed.  .  . 





51,  528  K. 

J.7  7^O  K 

14-05  K. 
16  ni  K 





"         hammered  bars,  soft.. 
Cast-steel   rivets,   English  (Moss  & 
Gamble).  .  ,  
Krupp's  bolt-steel  

Copper  



.00184  R. 

61,312  K. 

107,286  K. 
92,015  K. 

16.5    K. 

12.4    K. 
15.3    K. 



121,333  K. 

Sheets  

S<1Q  R. 

•20  ooo 

-i-i  OOO  A 

Cast  bars  

548.6  T.B. 

27,  800  T.B. 

6.47  T.B. 

42  oooT  B 

Bronze  

.00181  R. 

96.06C,    3-76T  

539.7  T.B. 

32,000  T.B. 

14.29  T.B. 

42  ooo  T  B 

92.nC,    7.80  T  
90.27C,    9-58T  
87.i5C,  I2.73T  
80.95  C,  18.847  
8  parts  copper,  i  part  tin  

542.5  T.B. 
540.9  T.B. 
541-7  T.B. 
545-6  T.B. 
524  R. 



28,540  T.B. 
26,  860  T.B. 
29,430  T.B. 
32,980  T.B. 
36,000  A. 

5-53  T.B. 
3.66  T.B. 
3-33  T.B. 
0.40  T.B. 



42,000  T.B. 
38,000  T.B. 
53,000  T.B. 
78,000  T.B. 

Brass  (rolled)  :  3  copper,  2  zinc  

525.4 

49,280  A. 

486.5 

.00216  R. 

28,900  A. 

A  =  Anderson  ;  H  =  Hodgkinson  ;   K  =  Kirkaldy  ;   R  =  Rankine  ;  W  =  Wade  ;  B  =  Brunei  ;  T.B  =  U.  S. 
Test  Board  ;  *  =  one  experiment. 


STEAM  BOILERS. 


CHAP.  IV. 


TABLE  XI. 
WEIGHT  OF  WROUGHT-IRON  PLATES  AND  BARS.     (Square  and  Round.) 

TRAUTWINE. 


Thickness  or  Diameter. 
Inches. 

Weight  of  plates  per  square 
foot,  in  pounds. 

Weight  per  foot  of  square 
bars,  in  pounds. 

Weight  per  foot  of  round 
oars,  in  pounds. 

i 

tt 

IO.IO 

n-37 
12.63 
13.89 

.2105 
.2665 
.3290 
.3980 

•  1653 
.2093 

-2583 
.3126 

1 
U 

15.16 
16.42 
17.68 
18.95 

-4736 
-5558 
.6446 
.7400 

.3720 
•4365 
•5063 
-5813 

! 

H 

20.  21 
22.73 
25.26 
27.79 

.8420 
1.  066 
1.316 

1-592 

.6613 

.8370 

1-033 
1.250 

if 

A 

3°-3I 
32.84 

35-37 
37-89 

I.89S 
2.223 

2-579 
2.960 

1.488 
1.746 
2.025 

2-325 

i 

TV 

J 

40.42 
42.94 

45-47 
48.00 

3-368 
3-803 
4.263 

4-75° 

2.645 
2.986 

3-348 

3-73° 

TV 
1 
TV 

5°-52 
53-°5 
55-57 
5810 

5-263 
5.802 
6.368 
6.960 

4.133 

4-557 
5.001 
5.466 

1 
3 

60.63 
65.68 
70-73 
75-78 

7-578 
8.893 
10.31 
11.84 

5-952 
6.985 
8.101 
9.300 

2 
i 

1 

80.83 
85.89 
9°-94 
95-99 

13-47 
15.21 

17-05 
19.00 

10.58 
"•95 

13-39 
14.92 

1 
* 

IOI.OO 

106.10 

III.  20 

116.20 

21.05 
23.21 

25-47 
27-84 

i6-53 
18.23 
20.  01 
21.87 

3 

121.30 

30-31 

23.81 

MATERIALS. 


85 


TABLE  XII. 
WEIGHT  OF  FLAT  BAR-IRON  PER  FOOT. 


Thickness  in  inches. 

Width  in 

inches. 

TV 

i 

A 

i 

A 

1 

A 

i 

* 

i 

i 

i 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

.21 

•42 

•63 

.84 

•°5 

1.26 

i-47 

1.68 

2.  II 

2-53 

2-95 

3-37 

-J- 

.24 

•47 

•7i 

•95 

.18 

1.42 

1.66 

1.90 

2-37 

2.84 

3-32 

3-79 

J 

.26 

•53 

•79 

•05 

•32 

1.58 

1.84 

2.I.I 

2.63 

3.16 

3.68 

4.21 

1 

.29 

•5» 

.87 

.16 

•45 

i-74 

2.03 

2.32 

2.89 

3-47 

4-05 

4-63 

£ 

•32 

•63 

•95 

.26 

•58 

1.90 

2.21 

2-53 

3.16 

3-79 

4.42 

5-05 

•| 

•34 

.68 

•°3 

•37 

•7i 

2.05 

2-39 

2-74 

3-42 

4.11 

4-79 

5-47 

1 

•37 

•74 

.11 

•47 

.84 

2.21 

2.58 

2-95 

3.68 

4.42 

5-i6 

5-89 

I* 

.40 

•79 

.18 

•58 

•97 

2-37 

2.76 

3.16 

3-95 

4-74 

5-53 

6.32 

2 

.42 

.84 

.26 

.68 

2.  II 

2-53 

2.95 

3-37 

4.21 

5-°5 

5-89 

6-74 

4 

•45 

.90 

•34 

•79 

2.24 

2.68 

3-J3 

3-58 

4-47 

5-37 

6.26 

7.16 

2± 

•47 

•95 

.42 

.90 

2-37 

2.84 

3-32 

3-79 

4-74 

5.68 

6.83 

758 

H 

•So 

I.OO 

•5° 

2.OO 

2.50 

3.00 

3-5° 

4.00 

5.00 

6.00 

7.00 

8.00 

,i 

•53 

1-05 

•58 

2.  II 

2.63 

3-i6 

3.68 

4.21 

5.26 

6.32 

7-37 

8-42 

«4 

•55 

I.  II 

.66 

2.21 

2.76 

3-32 

3-87 

4.42 

5-53 

6.63 

7-74 

8.84 

«i 

•58 

1.16 

•74 

2.32 

2.89 

3-47 

4-°5 

4-63 

5-79 

6-95 

8.10 

9.26 

4 

.61 

1.  21 

.82 

2.42 

3-°3 

3.63 

4.24 

4.84 

6.05 

7.26 

8.47 

9.68 

3 

•63 

1.26 

1.90 

2-53 

3.16 

3-79 

4.42 

5-°5 

6.32 

7,S8 

8.84 

IO.IO 

3f 

.68 

i-37 

2.05 

2-74 

3-42 

4.11 

4-79 

5-47 

6.84 

8.21 

9-58 

10.95 

4 

•74 

i-47 

2.21 

2-95 

3.68 

4.42 

S-i6 

5-89 

7-37 

8.84 

10.32 

11.79 

3* 

•79 

1.58 

2-37 

3.16 

3-95 

4-74 

5-53 

6.32 

7.89 

9-47 

11.05 

12.63 

4 

.84 

1.68 

2-53 

3-37 

4.21 

5-°5 

5-89 

6.74 

8.42 

IO.IO 

11.79 

13-47 

4* 

.90 

1.79 

2.68 

3.S8 

4-47 

5-37 

6.26 

7.16 

8-95 

10.74 

12-53 

I4-31 

4 

•95 

1.90 

2.84 

3-79 

4-74 

5.68 

6.63 

7-.S8 

9-47 

11.38 

13.26 

15.16 

4 

I.OO 

2.00 

3.00 

4.00 

5.00 

6  oo 

7.00 

8.00 

10.00 

I2.0O 

14.00 

16.00 

5 

1-05 

2.  II 

3.16 

4.21 

5.26 

6.32 

7-37 

8.42 

10-53 

12.63 

14-74 

16.84 

5f 

i.  ii 

2.21 

3-32 

4-42 

5-53 

6.63 

7-74 

8.84 

11.05 

13.26 

15-47 

17.68 

Si 

1.16 

2.32 

3-47 

4-63 

5-79 

6-95 

8.10 

9.26 

11.58 

1389 

16.21 

18.52 

si 

1.  21 

2.42 

3-63 

4-84 

6.05 

7.26 

8.47 

9.68 

12.10 

14-53 

16.95 

19-37 

6 

1.26 

2-53 

3-79 

5-°5 

6.32 

7.58 

8.84 

10.10 

12.63 

I5.l6 

17.68 

20.  21 

STEAM  BOILERS. 


CHAP.  IV. 


TABLE    XIII. 


WEIGHT  OF  SHEET  AND  PLATE  IRON. 


Thickness. 

Weight. 

Thickness. 

Weight. 

B.  W.  gauge. 

Fractions  of  an 
inch. 

Pounds  per  square 
foot. 

B.  W.  gauge. 

Fractions  of  an 
inch. 

Pounds  per  square 
foot. 

36 

.004 

.126 

II 

.120 

4.48 

35 

.005 

.202 

i  or.  125 

5^54 

34 

.007 

.283 

10 

•134 

5.426 

33 

.008 

.322 

9 

.148 

5-98 

32 

.009 

•364 

&  or.  1562 

6.305 

31 

.OIO 

.405 

8 

.165 

6.605 

3° 

.OI2 

•485 

7 

.180 

7.27 

29 

.013 

.526 

-fa  or.  1875 

7.578 

28 

.OI4 

•595 

6 

.203 

8.005 

27 

.Ol6 

.677 

-fa  or.  2187 

8-79 

26 

.018 

•755 

5 

.22 

8.912 

25 

.020 

.811 

4 

.238 

9.62 

24 

.022 

.912 

ior.25 

10.09 

23 

.025 

.018 

3 

•259 

10.37 

22 

.028 

•137 

-^  or  .2812 

11.38 

•S^or  -03125 

•259 

2 

.284 

11-525 

21 

.032 

•3i 

I 

•3 

12.15 

20 

•°35 

.416 

A  or  .3125 

12.58 

r9 

.042 

•695 

O 

•340 

13-75° 

18 

.049 

•075 

tt  or  .3437 

13.875 

17 

.058 

2-35 

1  or  .375 

15.10 

TV  or  .0625 

2.518 

oo 

.380 

15.26 

16 

.065 

2.637 

||  or  .4062 

16.34 

15 

.072 

2.92 

ooo 

•425 

17.125 

U 

.083 

3-35 

A  or  -4375 

17-65 

T&or  .0937 

3-78 

oooo 

•454 

18.30 

13 

•°9S 

3-85 

H  or  .4687 

18.90 

12 

.109 

4-4 

ooooo 

ior.5o 

20.00 

For  steel 'plates  multiply  the  tabular  number  of  any  size  by  i.oi. 


MATERIALS. 


87 


TABLE    XIV. 
WEIGHT  OF  WROUGHT  ANGLE-IRON.      (C.  W.  &>  H.  W.  Middleton,  Philadelphia) 


Dimension! 

in  inches. 

Weight  per  foot 

Width. 

Thickness. 

in  pounds. 

fx   | 

i 

t 

i     X  i 

4x4 
if  xij 

4x  4 

if  X  if 

A 

i  to  A 

A 
A  to  i 

i  to  ^ 

i    to    4 
ii  to    if 

4  tO       2 
if  tO      2± 

2}  to    4^ 

2X2 
2±X    4 
2*  X    2^ 
2\  X    2£ 
2f  X   2f 

i-  to  i 

A  to  f 

A  to  I 

•A-  to  | 
A  to  | 

3    to    5 
2ito    3 
4    to    6 
5    to  10 
6    to    8 

3      X2 
3       X    2\ 
3X3 

3iX  2 
3iX  3 

f  to* 

A  to  i 

1  to  i 
1  to  A 

4    to    5 
5i  to    8i 
7^  to  10 
6£  to    8 
7f  to  ii 

3*X3i 
4X3 
4    X  3i 
4X4 
4iX  3 

i  to  | 

1 
I  «°A 

1  to  | 

f_^A 

9    to  12 
8£  to  12 
9    to  13 
ii    to  15 
9    to  13 

5X3 

13 

5    X  3i 

n4 

5X4 

144  to  20 

6    X3i 
6X4 

I 

i  to  | 

22 

14    to  27 

6^X4 

A  to  | 

I4|  tO  20| 

STEAM  BOILERS. 


CHAP.  IV. 


TABLE  XV. 
WEIGHT  OF  WROUGHT  T-IRON-     (C-  W.  <&*  H.  W.  Middleton,  Philadelphia.} 


Dimensions  in  inches. 

Weight  per  foot  in  pounds. 

i     X  i 

ftoi 

itX  it 

l£  tO  2 

i£  X  it 

3 

ii  x  4 

2      tO  Z\ 

if  X  it 

3 

if  X  if 

2f 

2X2 

3: 

2|  X    2; 

3: 

2\  X    2 

5-' 

*\   X    2J- 

6; 

2|   X    I: 

6; 

3X3 

6^  to  9 

3    X  3^ 

i  of  to  ii 

3X4 

II       tO    12 

3T  X  3 

10    to  ii 

3^  X  3^ 

10    to  12 

3t  X  4 

i3i 

4    X  2 

6|  to  8 

4X4 

12 

4    X  4^ 

13 

4X5 

14 

5     X  2^ 

10  tO  12 

5    X  3 

II  tO  14 

MATERIALS. 


TABLE  XVI. 

WROUGHT-IRON  BOLTS  WITH  SQUARE  HEADS  AND  NUTS. 

(C.  W.  &  H.  W.  Middlcton,  Philadelphia.) 
Weight  in  pounds  of  100  of  the  enumerated  sizes. 


Lengths. 

Jin. 

1  in. 

i  in. 

|in. 

Jin. 

|in. 

i  in. 

i|in. 

Inches. 
ii 

10  62 

21  87 

•2Q  ^T 

1? 
i£ 

'O-0/ 

2*5  06 

oy-j* 

41.^8 

XT 

.44 

12  "IS 

AC  6O 

71  62 

24- 

•75 

28  62 

^o-"y 

AO.  CO 

/>>•"* 
76. 

2f 
2! 

•34 
5  .07 

IA  60 

2n  CO 

^•y-o" 

CI  21 

/"• 

7O.7C 

*X 
2$ 

•y/ 

6  t\o 

I  6  A.*J 

^y-j" 

7T  l6 

C1 

8l. 

*« 

3 
3i 

4 

4 

5 
5* 
6 
64 

•  •  •  • 

17.87 
18.94 
20.59 

21.69 

23.62 
25.81 
26.87 

32-44 
39-75 
42.50 
44.87 
48.81 
5I-38 
S3-3i 
e6  87 

oo- 
56. 
63.12 

74.87 
79.62 

83- 
87.88 

92-38 
96  88 

85-38 

93-44 
108.12 
113.12 

122. 
128.62 

I3'-75 

I  7O  c6 

127.25 
140.56 

148-37 
158.76 
167.25 
174.88 
204.25 

214  60 

228 

239 

250 

261 
272 
281 

•  •  • 

296 
310 
324 
338 
352 
166 

7 

CO  12 

00.87 

^oy';)" 

228.44 

2O4 

"?7O 

71 

oy-1* 
61  87 

yy*i 

IOC  7C 

*w*y 

150  88 

21C  11 

•»oc 

184 

/  S 

8 

64.44 

iu5-/  j 
IOQ  CO 

IC7.I2 

*o!3-JL 
210.88 

<JUJ 

116 

108 

7O.CO 

118  12 

160.62 

258  12 

^•?8 

426 

10 

77 

i  '8  ii 

184. 

276  18 

oo" 

16O 

4C.4 

ii 

82  88 

1  16  IO 

TOC.T  7 

-?82 

482 

12 

86  -17 

1-1/1.87 

1yo*1o 

2OO.  7C 

^yo-uy 
1  1  r  04 

0°^ 
AO4 

Clo 

H 

02 

I  CC  CO 

^"y'/D 

iic  81 

426 

J1" 

Cl8 

id. 

y- 

O7  71 

1  J  J'j" 

161  c8 

•*aro/ 

2  ?7  CO 

oo5'01 

ici  88 

AA& 

JO" 

c66 

I  d 

y/-/  3 

IO1  2C 

iuo-3" 

I7O  7C 

O/'J1-' 

OO1-00 
1OT  7C 

47O 

0"" 
CO4 

1  /"-/3 

oy1-/^ 

oyt 

90 


STEAM  BOILERS. 


CHAP.  IV. 


TABLE    XVII. 

STANDARD  SIZES  OF  WASHERS. 

(C.   W.  &  H.    W.  Middleton,  Philadelphia) 


Size  of  bolt. 

Diameter  of  washer. 

Size  of  hole. 

Thickness,  wire  gauge. 

Number  in  too  Ibs. 

Inch. 

Inch. 

Inch. 

No. 

i 

* 

A 

16 

29,300 

A 

$• 

-I 

16 

18,000 

i 

I 

A 

14 

7,600 

* 

«i 

A 

ii 

2,100 

,1 

1 

ii 

2,180 

xi 

•H 

ii 

2,35° 

if 

if 

ii 

i,  680 

2 

ft 

10 

1,140 

i 

•t 

,i 

8 

580 

2j 

1} 

8 

47° 

3 

» 

7 

360 

3 

X* 

6 

360 

or  TMC 
UNIVERSITY 

OF 


MATERIALS. 


91 


TABLE    XVIII. 


SHOWING  NUMBER  OF  "BURDEN'S"  RIVETS  IN  roo  POUNDS. 


Length  ir 

inches. 

%  inch  diameter. 

%  inch  diameter. 

11-16  inch  diameter. 

%  inch  diameter. 

i 

S 

1,092 
1,027 

665 

597 





940 

538 

45° 

.... 

840 

5'2 

415 

.... 

797 

487 

389 

356 

760 

460 

370 

329 

730 

440 

357 

28o 

711 

420 

34° 

271 

693 

39° 

325 

262 

648 

375 

3'2 

257 

2 

6c8 

360 

297 

243 

2- 

573 

354 

289 

237 

2; 

555 

347 

280 

232 

2; 

525 

335 

260 

220 

2i 

500 

3«2 

242 

208 

3 

460 

290 

224 

I97 

z\ 

t 

433 

267 

212 

180 

3: 

• 

4i3 

248 

201 

169 

IJ 

i 

395 

241 

I92 

160 

4 

23° 

184 

158 

4i 

r 

.... 

220 

'77 

'5° 

4: 

»  •  •  • 

210 

'7i 

146 

«j 

.... 

2OO 

1  66 

138 

5 

.... 

190 

161 

'35 

5^ 

t 

.... 

180 

156 

130 

SI 

! 

.... 

172 

164 

'5? 
'45 

124 

120 

6 

.... 

'57 

140 

"5 

<H 
fr 

I 

.... 

'5° 
146 

138 
'34 

in 
107 

61 

\ 

.... 

X43 

129 

104 

7 



140 

125 

too 

L 

CHAPTER  Y. 

TESTING  THE  MATERIALS. 

1.  General  Character  of  Tests.— The  tests  to  be  applied  to  materials  used  in 
the  construction  of  boilers  are  of  three  different  kinds— viz.,  first,  the  investigation  of 
the  mechanical  properties  of  the  materials  as  developed  in  the  testing-machine  ;  second- 
ly, the  trial  of  the  quality  of  the  materials  affecting  their  fitness  to  undergo  the  vari- 
ous mechanical  processes  employed  in  boiler-making  ;  thirdly,  the  search  for  imperfec- 
tions in  the  structure  of  the  materials  developed  in  the  process  of  manufacture. 

2.  United  States  Laws  and  Regulations  regarding  the  Tests  of  Boiler- 
plates.— The  '  Revised  Statutes  of  the  United  States '  prescribe  the  following  tests 
for  boiler-plates:  "Section  4430.  Every  iron  or  steel  plate  used  in  the  construction  of 
steamboat  boilers,  and  which  shall  be  subject  to  a  tensile  strain,  shall  be  inspected  in 
such  manner  as  shall  be  prescribed  by  the  Board  of  Supervising  Inspectors  and  ap- 
proved by  the  Secretary  of  the  Treasury,  so  as  to  enable  the  inspectors  to  ascertain  its 
tensile  strength,  homogeneousness,  toughness,  and  ability  to  withstand  the  effect  of 
repeated  heating  and  cooling  ;  and  no  iron  or  steel  plate  shall  be  used  in  the  construc- 
tion of  such  boilers  which  has  not  been  inspected  and  approved  under  those  rules. 

"Section  4431.  Every  plate  of  boiler-iron  or  steel  made  for  use  in  the  construction  of 
steamboat  boilers  shall  be  distinctly  and  permanently  stamped  by  the  manufacturer 
thereof,  and,  if  practicable,  in  such  places  that  the  marks  shall  be  left  visible  when  such 
plates  are  worked  into  boilers,  with  the  name  of  the  manufacturer,  the  place  where 
manufactured,  and  the  number  of  pounds  tensile  strain  it  will  bear  to  the  sectional 
square  inch." 

'  The  General  Rules  and  Regulations  prescribed  by  the  Board  of  Supervising  In- 
spectors of  Steam-vessels,'  January,  1879,  contain  the  following  instructions  regarding 
the  tests  to  be  applied  to  boiler-plates : 

"JRuleS.  Every  iron  or  steel  plate  intended  for  the  construction  of  boilers  to  be 
used  on  steam-vessels  shall  be  stamped  by  the  manufacturer  in  the  following  manner— 
viz.,  at  the  diagonal  corners,  at  a  distance  of  about  four  inches  from  the  edges,  and  also 
at  or  near  the  centre  of  the  plate,  with  the  name  of  the  manufacturer,  the  place  where 


SEC.  3.  TESTING  THE  MATERIALS.  93 

manufactured,  and  the  number  of  pounds  tensile  strain  it  will  bear  to  the  sectional 
square  inch. 

"  When  a  sheet  of  boiler-iron  is  found  by  the  inspector  with  one  or  more  stamps 
upon  the  same,  the  inspector  shall  in  every  such  case  be  governed  by  and  rate  the  ten- 
sile strain  of  iron  in  accordance  with  the  lowest  stamp  found  upon  the  same. 

"  Rule  4.  The  manner  of  inspecting  and  testing  boiler-plates  intended  to  be  used  in 
the  construction  of  marine  boilers,  by  the  United  States  inspectors,  shall  be  as  follows, 
viz.: 

"The  inspector  shall  visit  places  where  marine  boilers  are  being  constructed,  as 
often  as  possible,  for  the  purpose  of  ascertaining  and  making  a  record  of  the  stamps 
upon  the  material,  its  thickness,  and  other  qualities.  To  ascertain  the  tensile  strain 
[strength]  of  the  plates  the  inspector  shall  cause  a  piece  to  be  taken  from  each  sheet 
to  be  tested,  the  area  of  which  shall  equal  one-quarter  of  one  square  inch  on  all 
iron  ^  inch  thick  and  under  ;  and  on  all  iron  over  ^  inch  thick  the  area  shall  equal 
the  square  of  its  thickness,  and  the  force  at  which  the  piece  can  be  parted  in  the  direc- 
tion of  the  fibre  or  grain,  represented  in  pounds  avoirdupois — the  former  multiplied  by 
four,  the  latter  in  proportion  to  the  ratio  of  its  area — shall  be  deemed  the  tensile  strain 
per  square  inch  of  the  plate  from  which  the  sample  was  taken  ;  and  should  the  tensile 
strength  ascertained  by  the  test  equal  that  marked  on  the  plates  from  which  the  test- 
pieces  were  taken,  the  said  plates  must  be  allowed  to  be  used  in  the  construction  of  ma- 
rine boilers,  provided  always  that  the  said  plates  possess  the  other  qualities  required  by 
law— viz.,  homogeneousness,  toughness,  and  ability  to  withstand  the  effect  of  repeated 
heating  and  cooling ;  but  should  these  tests  prove  the  marks  on  the  said  plates  to  be 
overstamped,  the  lots  from  which  the  test-plates  were  taken  must  be  rejected  as  failing 
to  have  the  strength  stamped  thereon.  But  nothing  herein  shall  be  so  construed  as  to 
prevent  the  manufacturers  from  restamping  such  iron  at  the  lowest  tensile  strain  indi- 
cated by  the  samples,  provided  such  restamping  is  done  previous  to  the  use  of  the  plates 
in  the  manufacture  of  marine  boilers. 

"To  ascertain  the  ductility  and  other  lawful  qualities,  iron  under  45,000  pounds 
should  show  a  contraction  of  area  of  12  per  cent. ;  45,000  pounds  and  under  50,000 
should  show  15  per  cent.  ;  50,000  pounds  tensile  strength  and  over  should  show  25  per 
cent,  at  point  of  rapture." 

3.  The  Rodman  Testing-machine.— The  Eodman  Testing-machine  at  the  Ord- 
nance Department  of  the  Washington  Navy-Yard  has  been  used  in  making  several  of 
the  experiments  recorded  in  this  volume.  An  illustration  of  it  is  given  on  Plate  I.  It 
consists  essentially  of  a  system  of  three  levers,  A,  B,  and  C,  the  arms  of  which  have 


94  STEAM  BOILERS.  CHAP.  V. 

the  following  proportions  :  A  =  10  :  1 ;  B  =  20:l;  0  =  10:1;  consequently  the  total 
leverage  of  the  machine  is  2,000  :  1.  The  machine  is  capable  of  measuring  a  stress  of 
one  hundred  thousand  pounds,  and  is  arranged  to  determine  tensile,  compressive,  trans- 
verse, and  torsional  stresses,  as  well  as  indenting  forces  and  bursting  pressures  applied 
to  hollow  vessels. 

The  main  lever  A  acts  directly  upon  the  specimen  by  means  of  the  stirrup  D.  The 
fulcrum  F  of  the  main  lever  is  supported  by  a  pair  of  heavy  cast-iron  stanchions,  S  S, 
secured  by  bolts  to  the  bed-frame  T.  The  stirrup  D  bears  upon  the  lever  A  by  means 
of  the  knife-edge  a,  and  has  at  its  lower  end  a  shackle,  d,  to  which  the  various  con- 
trivances for  transmitting  the  stress  to  the  specimen  iinder  test  are  attached.  A  strap, 
E,  connects  the  main  lever  with  the  intermediate  lever  B,  which,  in  turn,  is  connected 
by  means  of  the  adjustable  rod  G  with  the  small  lever  C.  On  the  latter  are  placed  the 
weights  producing  the  stress  to  which  the  specimen  is  to  be  exposed.  The  lever  C  is 
graduated  from  0  to  10  and  carries  a  small  sliding-weight,  p  ;  by  moving  this  weight 
one  division  of  the  scale  out  from  the  fulcrum  a  stress  of  100  pounds  is  exerted  on  the 
specimen  attached  to  the  stirrup  D.  At  the  point  c,  corresponding  to  the  tenth  divi- 
sion, the  lever  C  carries  a  rod,  H,  on  which  additional  weights  can  be  placed  ;  of  these 
there  are  two  kinds — viz.,  ten  representing  a  stress  of  1,000  Ibs.  each,  and  nine  repre- 
senting a  stress  of  10,000  Ibs.  each  at  the  point  a. 

In  order  to  counterbalance  exactly  the  weight  of  the  levers  and  their  attachments 
the  weights  V  and  V  can  be  moved  in  or  out  on  the  rods  passing  through  their  centre ; 
V  being  attached  directly  to  the  lever  C,  while  V  acts  by  means  of  a  lever  and  strap  on 
the  intermediate  lever  B.  In  order  to  reduce  the  friction  to  a  minimum  case-hardened 
steel  knife-edges  are  used  for  the  bearings  of  the  levers  and  their  connections. 

It  is  evident  that  any  movement  of  the  point  d  on  the  lever  A,  caused  by  the  elonga- 
tion, compression,  or  deflection  of  the  specimen,  is  increased  two-thousandfold  at  the 
point  c  of  the  lever  C ;  it  is,  however,  essential  to  maintain  the  levers  in  an  exactly 
horizontal  and  parallel  position,  since  otherwise  the  leverage  of  the  machine  would  be 
altered,  and  its  balance  would  be  disturbed  by  shifting  the  centre  of  gravity  of  the 
levers.  On  this  account  the  fulcrums  /and  ./'  of  the  levers  B  and  C  are  attached  to 
the  sliding-blocks  g  and  g',  which  can  be  moved  up  or  down  by  suitable  gearing.  The 
hand-crank  N  turns,  through  the  intervention  of  a  train  of  wheels  and  pinions,  the 
horizontal  wheel  O,  which,  in  turn,  gives  motion  to  the  screw  R,  the  central  boss  of 
the  wheel  forming  a  nut  for  the  screw  ;  the  lower  end  of  the  latter  is  attached  to  the 
sliding-block  g,  which  is  guided  between  the  frames  Z  Z.  To  this  block  is  attached 
the  rack  7i,  gearing  with  a  pinion  fastened  on  the  shaft  J  which  carries,  on  its  other  end. 


SEC.  3. 


TESTING  THE  MATERIALS.  95 


a  corresponding  pinion,  i ',  gearing  with  the  rack  Ji ' ;  the  latter  is  attached  to  the  slid- 
ing-block  g',  which  is  guided  between  brackets  forming  part  of  the  stanchions  S  S. 
In  this  manner  the  vertical  motion  of  the  fulcrum  /  of  the  lever  B  is  communicated  to 
the  fulcrum  /'  of  the  lever  C,  and  the  horizontally  and  perfect  parallelism  of  the  two 
levers  can  be  maintained.  No  means  are  provided  to  keep  the  main  lever  in  a  horizon- 
tal position  during  the  operation  of  the  machine,  but  the  error  arising  from  this  source 
is  trifling,  since  this  lever  has  always  only  a  comparatively  slight  motion.  In  order 
that  the  disturbance  of  the  balance  of  the  machine  in  consequence  of  the  motion  of  the 
centre  of  gravity  of  the  lever  A  be  as  small  as  possible,  the  lever  has  received  such  a 
shape  that  its  centre  of  gravity  lies  near  its  centre  of  motion. 

The  large  screw  U,  placed  directly  under  the  point  a,  passes  through  the  bed-frame 
and  can  be  adjusted  to  a  proper  height  by  means  of  a  hand-wheel.  Its  upper  end  is 
provided  with  a  suitable  arrangement  for  holding  the  specimen  subjected  to  a  tensile 
strain  or  the  straps  used  in  applying  compressive  and  indenting  forces. 

When  transverse  strains  are  to  be  produced  the  two  movable  pedestals,  X  X,  at- 
tached to  the  bed-frame  are  used.  They  are  fitted  with  knife-edges,  against  which  the 
test-bar  bears,  the  strain  being  applied,  by  a  strap  connected  to  the  stirrup  D,  to  the 
lower  side  of  the  bar. 

Torsional  strains  are  measured  by  means  of  the  lever  M,  which  works  between  the 
two  pillow-blocks,  Y  Y,  secured  to  the  bed-frame.  The  hollow  axis  of  this  lever  receives 
the  specimen,  the  projecting  ends  of  which  are  firmly  secured  by  cotters  to  the  blocks. 
The  lever  M  is  connected  by  means  of  a  chain  and  link  to  the  intermediate  lever  B.  A 
graduated  arc  is  attached  to  the  pillow-block  Y,  and  a  pointer  connected  with  the  axis 
of  the  lever  indicates  the  number  of  degrees  through  which  the  specimen  has  been 
twisted. 

Before  beginning  an  experiment  the  machine  is  balanced  by  a  proper  adjustment 
of  the  weights  V  and  V,  so  that  the  weights  placed  on  the  lever  C  measure  accurately 
the  stress  applied  to  the  specimen.  When  a  specimen  has  been  put  in  place  to  test  its 
tensile  or  compressive  strength  care  is  taken  that  all  lost  motion  is  taken  up  by 
moving  the  screw  U  up  or  down,  while  the  lever  C  is  kept  in  a  horizontal  position. 
Then  the  hand-crank  is  turned  with  regularity  in  a  direction  which  raises  the  screw  R, 
and  through  it  the  fulcrums  /  and  /',  while  at  the  same  time  the  sliding- weight  p  is 
moved  so  as  to  keep  the  lever  C  in  an  exactly  horizontal  position.  Whenever  the 
sliding- weight  p  registers  a  strain  of  1,000  Ibs.,  one  of  the  large  weights,  P,  represent- 
ing an  equivalent  strain,  is  substituted  for  it  on  the  rod  H,  and  the  sliding- weight  is 
moved  back  to  the  zero-point.  In  the  same  manner  a  weight,  P',  representing  a  strain 


96 


STEAM  BOILERS. 


CHAP.  V. 


of  10,000  Ibs.,  is  placed  on  the  rod  H  in  the  place  of  ten  weights  of  1,000  Ibs.  each.  By 
repeating  these  operations  the  effects  of  increments  of  100  Ibs.  each,  tip  to  the  limit  of 
100,000  Ibs.,  can  be  observed  and  measured. 

4.  Form  and  Dimensions  of  Test-specimens. — The  sectional  area  of  specimens 
that  are  to  be  tested  is  limited  by  the  strength  of  the  machine.  It  is  very  convenient 
to  give  such  dimensions  to  the  specimen  that  its  sectional  area  is  a  simple  multiple  or 
fraction  of  a  square  inch. 

It  is  found  that  long  bars  generally  stretch  more,  in  proportion  to  their  length,  than 
short  ones  of  the  same  material,  sectional  area,  and  form.  In  order  to  secure  greater 
uniformity  in  the  conditions  of  tests  the  French  Government  established  the  rule  that 
the  length  of  all  specimens  subjected  to  tests  of  tensile  strength  should  be  200  milli- 
metres (7.875  inches)  between  the  shoulders  ;  and,  following  this  precedent,  the  English 
Admiralty  has  adopted  a  standard  length  of  8  inches. 


Fig.  1. 


Figures  1  and  2  show  the  forms  usually  given  to  specimens.  The  middle  portion, 
which  is  the  part  to  be  tested,  must  be  carefully  turned  or  planed,  as  the  case  may  be, 
to  the  exact  dimensions  required,  so  as  to  have  the  sides  perfectly  parallel.  It  is 
essential  that  the  strain  be  applied  exactly  in  the  direction  of  the  axis  of  the  specimen. 
In  order  to  measure  the  elongation  of  the  specimen  under  strain  its  length  is  divided 
by  lines  or  centre-punch  marks  into  equal  spaces.  Kirkaldy  described  on  the  surface 
of  some  specimens  a  network  of  diagonal  lines  or  circles,  the  distortion  of  which  repre- 
sented the  relative  elongation  of  different  portions  of  the  specimen.  Specimens  of  very 
thin  plates  may  have  side-plates  riveted  to  their  ends  to  give  them  longer  bearings  on 
the  pins  of  the  shackles.  Specimens  subjected  to  a  crushing  strain  are  seldom  made 
longer  than  twice  their  diameter. 

The  influence  of  length  and  form  on  the  apparent  strength  of  test-specimens  is  illus- 
trated by  "  the  results  of  a  series  of  trials  of  samples  of  steel  cut  from  the  same  plate 
and  reduced  in  width  as  shown"  (see  figures  3  and  4),  given  by  Keed  in  '  Shipbuilding 
in  Iron  and  Steel,'  pp.  401,  402.  "Eight  cases  were  taken,  each  case  being  tested  by 
three  experiments  for  each  mode  of  reduction.  The  breaking  section  was  in  each  case 


SBC.  5.  TESTING  THE  MATERIALS.  97 

reduced  to  a  breadth  of  one  inch,  the  reduction  from  the  extreme  breadth  of  the 
samples  (2J  inches)  being  made  in  one  set  of  plates  by  circular  arcs,  and  in  the  other 


Fig.  3. 


Fig.  4. 


set  by  parallel  reductions.  The  lengths  of  the  reduced  parts  were  varied  from  8  inches 
to  1  inch  by  successive  deductions  of  1  inch,  and  the  sketches  (figures  3  and  4)  show 
the  extreme  cases  of  the  longest  and  shortest  reductions  respectively.  The  forms  of  the 
circular  arcs  are  shown  in  ticked  lines,  and  those  of  the  parallel  reduction  by  drawn 
lines."  .  .  .  "Throughout  these  experiments,  which  were  conducted  with  extreme 
care,  the  same  material  broke  at  a  less  strain  when  trimmed  down  to  a  parallel  breadth 
for  a  considerable  distance  than  when  reduced  to  the  same  breadth  at  one  place  only. 
By  comparing  the  samples  reduced  to  a  parallel  breadth  for  a  length  of  8  inches  with 
those  similarly  reduced  for  a  length  of  1  inch  only,  it  will  be  seen  that  the  apparent 
strength  rose  from  an  average  of  19J  tons  to  an  average  of  21f  tons  ;  or  if  we  compare 
the  former  with  the  case  of  the  shortest  circular  reduction,  we  find  it  increasing  from 
19 J  tons  to  an  average  of  23f  tons." 

Numerous  experiments  were  also  made  by  the  United  States  Test  Board  to  deter- 
mine the  proper  form  and  dimensions  of  test-pieces.  The  results  of  these  experiments 
are  summed  up  in  the  report  of  the  Board  in  the  following  words :  "  In  conclusion, 
our  results  lead  us  to  the  decision  that  in  testing  [wrought]  iron  no  test-piece  should  be 
less  than  f  inch  diameter,  as  inaccuracy  is  more  probable  with  a  small  than  with  a  large 
piece,  and  the  errors  are  more  increased  by  reduction  to  the  square  inch ;  that  the 
length  should  not  be  less  than  four  times  the  diameter  in  any  case,  and  that  with  soft, 
ductile  metal  five  or  six  diameters  would  be  preferable." 

In  preparing  the  specimens  care  must  be  taken  that  the  metal  does  not  receive  in- 
jury impairing  its  strength.  On  this  account  they  should  be  cut  from  the  plate  by  saw- 
ing or  drilling,  and  then  filed  down  to  the  exact  dimensions.  In  case  punching  is  re- 
sorted to  it  is  necessary  to  leave  a  siirplus  of  metal  for  planing  or  filing  down,  in  order 
that  the  specimen  may  not  be  weakened  by  the  injury  which  the  metal  receives  in  the 
vicinity  of  a  punched  hole. 

5.  Effects  produced  by  Stress. — Under  a  gradually  increasing  tensile  stress  the 
elongation  of  metals  may  be  assumed  to  be  in  the  direct  ratio  of  the  stress,  within  the 
limit  of  elasticity,  and  whenever  the  stress  is  discontinued  the  specimen  will  resume 


98  STEAM  BOILERS.  CHAP.  V. 


very  nearly  its  original  dimensions.  The  elongation  of  wrought-iron  is  about  -nnb7  part 
of  its  length  for  every  ton  of  tensile  stress  per  square  inch  of  sectional  area,  and  its  limit 
of  elasticity  lies  between  8  and  12  tons  of  tensile  strain  per  square  inch.  A  bar  which 
has  been  strained  beyond  the  limit  of  elasticity,  and  has  in  consequence  taken  a  perma- 
nent set  after  the  stress  had  been  removed,  will  show  a  much  smaller  rate  of  elongation 
for  all  stresses  less  than  that  which  produced  the  set. 

Anderson  says  :  "A  bar  of  wrought-iron,  when  it  leaves  the  rolls,  is  in  a  condition  of 
great  restraint  ;  the  exterior  is  not  in  perfect  equilibrium  with  the  interior  of  the  bar, 
which  at  the  commencement  of  an  experiment  affects  the  elongation  and  permanent  set. 
The  first  effect  of  the  application  of  a  load  is  to  liberate  the  constrained  surface,  and 
true  conditions  on  which  to  form  an  opinion  do  not  exist  until  equilibrium  is  estab- 
lished in  the  bar  itself.  Previous  to  that  the  result  is  deceptive  ;  hence  the  advantage 
of  carefully-turned  specimens." 

Soft  and  ductile  materials  are  drawn  out  to  a  much  smaller  diameter  at  and  near  the 
point  of  fracture  before  the  final  rupture  takes  place.  Kirkaldy  was  the  first  to  point 
out  the  importance  of  calculating  the  ultimate  breaking  stress  per  square  inch  for  the 
contracted  area  at  the  point  of  fracture  as  a  measure  of  the  quality  of  the  material. 

Fibrous  wrought-iron  is  stronger  and  stretches  more  in  the  direction  of  the  fibres 
than  across  them  ;  hence  the  importance  of  cutting  test-specimens  of  boiler-plate  in  both 
directions  from  the  sheet. 

The  molecular  changes  of  a  ductile  material,  when  strained,  may  be  compared  to 
those  occurring  during  the  flow  of  liquids. 

Anderson  says:  "When  a  bar  is  drawn  out  the  principal  flow  of  the  apparently 
solid  metal  is  in  the  middle  of  the  stream,  and  hence  the  peculiar  sectional  form  which 
is  assumed  either  by  a  round  or  square  bar,  or  one  of  any  other  shape,  showing  that 
the  farther  the  molecules  of  the  material  are  removed  from  the  centre  of  the  flowing 
current,  so  much  the  less  are  they  affected  by  the  influence  of  the  general  movement. 
This  unequal  flowing  of  the  molecules  may  partly  account  for  the  apparent  weakness 
of  thin  plates  as  compared  with  round  bars  of  the  same  sectional  area." 

"  With  a  flowing,  malleable,  or  ductile  metal  the  round  bar,  when  under  tension,  is 
drawn  out  to  a  small  diameter  uniformly  all  around,  but  the  metal  goes  in  the  middle 
chiefly,  and  the  outside  is  shrivelled  ;  while  with  a  rectangular  or  square  bar  the  flat 
surfaces  are  slightly  hollowed  to  an  extent  proportionate  to  their  distances  from  the 
centre  of  the  flow." 

6.  Experiments  on  the  E.ffects  of  Hammering  and  Rolling  011  the 
Strength  of  Bars.  —  "  Early  in  the  course  of  the  mechanical  tests  [of  the  United  States 


SEC.  6. 


TESTING  THE  MATERIALS. 


Test  Board]  it  became  evident  that,  although,  each  set  of  nine  bars  (1  inch  to  2  inches 
diameter)  from  any  maker  was  made  of  the  same  material  and  as  uniformly  as  ordinary 
processes  would  allow,  yet  there  was  a  notable  variation  in  the  physical  characteristics 
of  the  different-sized  bars.  The  tenacity,  elastic  limit,  and  ductility  increased  as  the 
diameter  decreased.  In  fourteen  sets  of  bars  the  strength  per  square  inch  of  the  1-inch 
over  the  2-inch  ran  from  4,000  to  7,000  Ibs. ;  and  in  bars  known  to  have  had  uniform 
treatment  it  averaged  5,600  Ibs.  But  the  increase  of  strength  was  not  uniform.  In 
eight  sets  of  bars  the  strength  fell  off  at  the  1^-inch  size. 

"  An  investigation  of  the  method  of  manufacture  revealed  the  causes  of  these  phe- 
nomena. The  piles  from  which  the  2-inch,  If-inch,  If-inch,  and  If-inch  bars  were 
rolled  had  the  same  cross-section,  differing  only  in  length.  The  piles  from  the  1^-inch, 
If -inch,  IJ-inch,  and  1^-inch,  and  sometimes  the  1-inch,  were  of  the  same  area,  al- 
though smaller  than  the  piles  above  mentioned.  The  areas  of  the  piles  remaining  con- 
stant with  each  set,  while  those  of  the  bars  decreased,  the  smaller  bars  received  the  most 
work  in  the  rolls.  It  was  then  found  by  numerous  experiments  that  the  tenacity  and 
elastic  limit  of  the  various  bars  of  a  set  increased  just  in  proportion  to  the  decrease  of 
the  percentage  of  the  area  of  the  bar  to  that  of  the  pile. 


TABLE  XIX. 


Size  of  bar. 

Iron  AT,  showing  decrease  of  strength  by  decrease  of 
reduction. 

Iron  /lr,  showing  uniformity  of  strength  with  uniformity 
of  reduction. 

Area  of  bar  in  per 
cent,  of  area 
of  pile. 

Tensile  strength. 

Elastic  limit. 

Area  of  bar  in  per 
cent,  of  area 
of  pile. 

Tensile  strength. 

Elastic  limit. 

Inches. 

Per  cent. 

Pounds  per  square 
inch. 

Pounds  per  square 
inch. 

Per  cent. 

Pounds  per  square 
inch. 

Pounds  per  square 
inch. 

(Pile  6"  X  4%".) 

2 

4 
if 

if 

11.36 
10.22 
8-90 
7.68 

51,848 
54,034 
55'OlS 

56-344 

32,461 
33.610 
34-283 

35>889 

3-92 

3-45 
3-34 
3-24 

50,763 
53-361 

53.!54 
53,329 

33,258 
35-032 
35-323 
33-520 

(Pile  4"  X  3%".) 

0+-'*f-Qo)W«Sf-' 

11.78 
9.90 
8.18 
6.62 

53-550 
54.277 
56,478 
56.543 

34.690 
33-622 

33.251 
32.267 

i 

3-2? 
3-53 
3-4i 
3-3i 
3,4 

52,819 
52,733 
53-248 
54,645 
53,9r5 

34,840 
34,606 

33-520 

34-695 
36,287 

100 


STEAM  BOILERS. 


CHAP.  V. 


"  In  order  to  determine  if  the  converse  is  true  another  set  of  experiments  was  under- 
taken, and  it  proved  that,  by  preserving  a  uniform  proportion  of  bar  to  pile,  all  the  bars 
of  the  series  have  substantially  the  same  strength  per  square  inch. 

"Table  XIX.  gives  two  typical  examples,  selected  from  the  records  of  the  Board. 
That  of  iron  N  shows  the  effect  of  variation  in  the  percentages  of  pile  to  bar ;  that  of 
iron  Fx  the  effect  of  uniformity."  (A.  L.  Holley,  '  The  Strength  of  Wrought-iron  as 
affected  by  its  Composition  and  by  its  Reduction  in  Rolling?} 

In  the  Report  of  the  Committee  on  Chain-cables,  Malleable  Iron,  etc.,  of  the 
United  States  Test  Board,  it  is  stated  that,  although  the  strength  of  the  entire  bar  was 
increased  by  the  extra  work  in  rolling  the  bar  from  a  larger  pile,  yet  that  of  the  core  of 
the  iron  was  not,  as  shown  by  the  following  tests  : 

TENSILE  STRENGTH  AND  ELASTIC  LIMIT  OF  THREE  BARS,  IRON  Fx,  AS  FOUND  BY  RUPTURE  OF 

ENTIRE  BARS  AND  OF  TURNED  CYLINDERS. 


Size. 
Inches. 

Area  of  entire  bars  in 
per  cent,  of  area  of 
piles. 

Tensile  strength. 

Elastic  limit. 

Entire  bar. 

Cylinder. 

Entire  bar. 

Cylinder. 

Pounds  per  sq.  inch. 

Pounds  per  sq.  iirch. 

Pounds  per  sq    inch. 

Pounds  per  sq.  inch. 

2 

3-93 

52,011 

45,964 

34,702 

31,830 

'* 

I 

3-45 

2.62 

53,537 

55,77° 

47,i24 
49,656 

34,235 
34,279 

32,070 
35,714 

Plate  II.  contains  the  record  of  experiments  conducted  by  Chief -Engineer  Wm.  H. 
Shock,  U.  S.  N.,  which  are  instructive  in  showing  the  effect  of  an  increased  amount  of 
hammering  and  rolling  on  the  tenacity  and  ductility  of  a  bar  of  wrought-iron. 

The  test-specimens  were  all  cut  from  the  same  bar,  which  was  of  good  marketable 
American  iron,  4  inches  square.  One  end  of  the  bar  was  drawn  down  by  hammering  to 
a  size  of  2J  inches  square.  The  diagrams  on  Plate  II.  show  from  which  particular  por- 
tion of  the  bar  each  specimen  was  cut.  The  specimens  were  carefully  turned  to  the 
exact  size  given  on  the  plate,  and  were  subjected  to  a  tensile  strain  in  the  Rodman  Test- 
ing-machine represented  on  Plate  I. 

Comparing  the  results  obtained  with  specimens  cut  from  different  portions  of  the 
bar,  we  find :  First,  that  the  mean  tensile  strength  of  the  eight  specimens  marked  E, 
which  were  cut  from  the  sides  of  the  bar,  was  2. 13  per  cent,  greater  than  that  of  the  four 
specimens  marked  D,  which  were  cut  from  the  centre  of  the  bar  ;  and  that  the  mean 
elongation  of  the  former  was  16.1  per  cent,  greater  than  that  of  the  latter.  Secondly, 


SBC.  7.  TESTING  THE  MATERIALS.  101 

that  the  mean  tensile  strength  of  the  six  specimens  marked  A,  which  were  cut  from  the 
reduced  end  of  the  bar,  was  5.63  per  cent,  greater  than  that  of  the  specimens  marked 
D  ;  and  that  the  mean  elongation  of  the  former  was  9.79  per  cent,  greater  than  that  of 
the  latter.  Thirdly,  that  the  mean  tensile  strength  of  the  eight  specimens  marked  B 
and  C,  which  were  cut  across  the  fibre  of  the  bar,  was  40.85  per  cent,  less  than  that 
of  the  specimens  marked  D  ;  and  that  they  broke  without  showing  any  elongation. 
Fourthly,  that  the  several  specimens  marked  B  and  C  broke  under  widely  different 
strains  :  the  lowest  result  obtained  (specimen  Bl)  was  33.73  per  cent,  less  than  the  mean 
result  obtained  with  the  eight  specimens  of  classes  B  and  C  ;  and  the  highest  result  ob- 
tained (specimen  B2)  was  35.51  per  cent,  greater  than  the  mean  result.  Specimens  Bl 
and  B2  were  cut  from  immediately  adjoining  portions  of  the  bar.  The  highest  and  low- 
est breaking  strains  obtained  with  specimens  of  class  D  differ  less  than  one  per  cent, 
from  the  mean  result ;  and  with  specimens  of  class  E  this  difference  is  only  a  fraction 
more  than  one  per  cent.  The  difference  of  the  results  obtained  with  specimens  of  class 
A  is  equally  slight,  with  the  exception  of  specimen  A6,  which  broke  under  a  strain 
4.08  per  cent,  higher  than  the  mean  breaking  strain  of  class  A.  The  portion  of  the  bar 
from  which  A6  was  cut  had  prpbably  received  a  greater  amount  of  hammering  at  a 
lower  temperature  ;  this  assumption  appears  to  be  confirmed  by  the  smaller  amount  of 
elongation  of  this  specimen  before  rupture  occurred. 

7.  Appearance  of  Fractures. — The  fracture  of  iron  and  steel  should  present  a 
close,  uniform  grain  of  a  bright  gray  color,  or  a  silky  fibre  ;  when  of  a  dull,  earthy  as- 
pect, with  a  loose  texture,  an  unequal  grain,  or  a  blackish  fibre,  it  indicates  an  inferior 
quality  or  a  badly-refined  material. 

Fractures  of  steel  may  be  classified  as  granular,  crystalline,  and  fibrous,  and  those 
of  wrought-iron  as  crystalline  and  fibrous,  with  intermediate  gradations.  Hard,  un- 
yielding materials  always  present  a  granular  or  crystalline  fracture. 

With  respect  to  wrought-iron  Kirkaldy  deduces  the  following  results  from  Ms  expe- 
riments :  "1st.  "Whenever  wrought-iron  breaks  suddenly  a  crystalline  appearance  is 
the  invariable  result ;  when  gradually,  invariably  a  fibrous  appearance.  2d.  Whether, 
on  the  one  hand,  it  is  finely  or  coarsely  crystalline,  or,  on  the  other,  the  fibre  be  fine  or 
close,  or  coarse  and  open,  depends  upon  the  quality  of  the  iron.  3d.  When  there  is  a 
combination  in  the  same  bar  or  plate  of  two  kinds — the  one  harder  or  less  ductile  than 
the  other — the  appearance  will  be  partly  crystalline  and  partly  fibrous.  .  .  .  5th.  The 
relative  qualities  of  various  irons  may  be  pretty  accurately  judged  of  by  comparing  their 
fractures,  provided  they  have  all  been  treated  in  precisely  the  same  way,  and  all  bro- 
ken under  the  same  sort  of  strains  similarly  applied.  6th.  By  varying  either  the 


102  STEAM  BOILERS.  CHAP.  V. 

shape,  the  treatment,  the  kind  of  strain,  or  its  application,  pieces  cut  off  the  same  bar 
will  be  made  to  present  vastly  different  appearances  in  some  kinds  of  iron,  whilst  in 
others  little  or  no  difference  will  result.  .  .  . 

"The  appearance  of  the  same  bar  may  be  completely  changed  from  wholly  fibrous  to 
wholly  crystalline,  .  .  .  1st,  by  altering  the  shape  of  the  specimen  so  as  to  render  it 
more  liable  to  snap  ;  2d,  by  treatment  making  it  harder ;  and,  3d,  by  applying  the  strain 
so  suddenly  as  to  render  it  more  liable  to  snap  from  having  less  time  to  stretch.  .  .  . 

"  In  the  case  of  the  fibrous  fracture  the  threads  are  drawn  out  and  are  viewed  exter- 
nally ;  in  the  case  of  the  crystalline  fracture  the  threads  in  clusters  are  snapped  across, 
and  are  viewed  internally  or  sectionally.  .  .  , 

"The  conclusions  respecting  wrought-iron  are  equally  appropriate  to  steel — viz.: 
Whenever  rupture  occurs  slowly  a  silky  fibrous,  and  when  suddenly  a  granular,  ap- 
pearance are  invariably  the  result ;  both  kinds  varying  in  fineness  according  to  quality. 
The  surface  in  the  latter  case  is  even,  and  always  at  right  angles  with  the  length  ;  in 
the  former  angular  and  irregular  in  outline.  The  color  is  a  light  pearl  gray,  slightly 
varying  in  shade  with  the  quality ;  the  granular  fractures  are  almost  entirely  free  of 
lustre,  and  consequently  totally  unlike  the  brilliant  crystalline  appearance  of  wrought- 
iron." 

8.  Hot  and  Cold  Forge-tests. — The  forge-tests  applied  to  boiler-plates  used  in 
the  United  States  naval  service  vary  according  to  the  judgment  of  the  superintending  or 
inspecting  officers.  The  specifications  generally  require  that  the  plates  must  be  able  to 
bear  the  severest  flanging-tests  to  which  they  may  be  subjected.  These  consist  in  turn- 
ing flanges  on  two  adjacent  sides  of  a  plate,  thus  forming  a  corner ;  in  cutting  a  hole  in 
the  middle  of  a  plate  and  enlarging  it  by  turning  a  flange  up  around  it ;  in  giving  a 
dished  shape  to  the  plate  by  forcing  it,  by  means  of  a  jack  and  a  spherical  die,  into  a  cor- 
responding form.  The  plates  are  further  tested  cold  by  punching  holes  near  the  edges, 
and  by  bending  them  to  angles  of  different  degrees,  according  to  the  thickness  of  the 
plates.  They  must  bear  these  several  tests  without  showing  any  signs  of  cracks  or  lami- 
nations. 

In  the  English  service  the  iron  supplied  by  the  manufacturers  has  to  iindergo  the 
tests  described  in  section  11,  chapter  vii.,  which  are  carried  out  in  the  same  manner,  as 
nearly  as  possible,  in  the  various  establishments,  both  private  and  public,  under  the  su- 
pervision of  Admiralty  officers.  In  applying  the  bending-tests  it  is  prescribed  that 
plates,  both  hot  and  cold,  should  be  tested  on  a  cast-iron  slab,  having  a  fair  surface, 
with  an  edge  at  right  angles,  the  corner  being  rounded  off  with  a  radius  of  £  inch. 
The  plate  should  be  bent  at  a  distance  of  from  3  to  6  inches  from  the  edge. 


SEC.  9.  TESTING  THE  MATERIALS.  103 

Wilson  says:  "All  plates  of  the  very  best  quality,  having  a  longitudinal  tenacity 
of  24  tons  per  square  inch  of  section  and  an  ultimate  elongation  of  about  12  per  cent., 
and  not  exceeding  one  inch  in  thickness,  should  bend  double  along  or  across  the  fibre 
when  red-hot. 

"For  the  cold  forge-test  plates  of  the  very  best  quality  ^  inch  thick  and  under 
should  bend  double  without  fracture.  .  .  . 

"  The  angle  to  which  the  plates  can  be  bent  without  fracture  will  depend  greatly 
upon  the  skill  of  the  smith  who  heats  and  operates  upon  them.  A  plate  that  will  bear 
the  test  with  a  number  of  sharp,  light  blows  will  often  fail  when  a  heavy  hammer  is 
used.  By  striking  the  plate  along  its  surface  it  can  be  successfully  bent  to  a  much 
greater  angle  than  when  the  blows  are  dealt  perpendicularly  to  the  surface. 

"The  plate  will  also  stand  the  bending  much  better  if  it  is  performed  uniformly 
along  its  whole  width.  .  .  .  The  manner  in  which  a  plate  will  bear  flanging  out- 
wardly, whereby  the  fibres  are  either  stretched  or  separated,  as  the  plate  is  flanged 
across  or  along  the  grain,  is  generally  considered  the  best  test  of  its  soundness  and 
quality.  .  .  . 

"  Rivets  and  bars  for  boiler- work  are  seldom  tested  for  their  tensile  strength,  but 
their  quality  is  usually  ascertained  by  the  forge-tests.  A  good  rivet,  cold,  will  bend 
double  without  fracture.  The  head  of  a  good  rivet  should  flatten  out,  by  hammering 
when  hot,  to  about  £*  thick,  without  fracture  or  fraying  at  the  edge.  A  hot  rivet-shank 
or  bar  of  iron,  when  flattened  down  to  a  thickness  equal  to  about  one-half  its  diameter, 
should  bear  a  punch  driven  through  it  without  fracture  at  the  hole." 

9.  Directions  for  testing  Bar-iron. — "Cut  a  notch  on  one  side  with  a  cold- 
chisel,  then  bend  the  bar  over  the  edge  of  an  anvil  at  sharp  angles.  If  the  fracture  ex- 
hibits long,  silky  fibres  of  a  leaden  gray  color,  cohering  together,  and  twisting  or  pull- 
ing apart  before  breaking,  it  denotes  tough,  soft  iron,  easy  to  work  and  hard  to  break. 
In  general  a  short,  blackish  fibre  indicates  iron  badly  refined.  A  very  fine,  close  grain 
denotes  a  hard,  steely  iron,  which  is  apt  to  be  cold-short,  but  working  easily  when 
heated,  and  making  a  good  weld.  Numerous  cracks  on  the  edges  of  the  bar  generally 
indicate  a  hot-short  iron,  which  cracks  or  breaks  when  punched  or  worked  at  a  red 
heat,  and  will  not  weld.  Blisters,  flaws,  and  cinder-holes  are  caused  by  imperfect 
welding  at  a  low  heat,  or  by  iron  not  being  properly  worked,  and  do  not  always  indicate 
inferior  quality. 

"  To  test  iron  when  hot,  draw  a  piece  out,  bend  and  twist  it,  split  it,  and  turn  back 
the  two  parts  to  see  if  the  split  extends  up ;  finally  weld  it,  and  observe  if  cracks 
or  flaws  weld  easily.  Good  iron  is  frequently  injured  by  being  unskilfully  worked ; 


104  STEAM  BOILERS.  CHAP.  V. 

defects  caused  by  this  may  be  in  part  remedied.     If,  for  example,  it  has  been  injured 
by  cold-hammering  moderate  annealing  heat  will  restore  it."     (King.} 

10.  Testing  Steel  Boiler-plates. — For  steel  boiler-plates  the  following  tests  are 
prescribed  by  the  French  Government:    "Hot  tests:  These  tests  will  be  made  with 
sample  plates  of  suitable  dimensions,  and  consist  in  stamping  a  dished  cavity,  the  side 
of  the  plates  preserving  its  original  plane.     The  diameter  of  this  cavity  is  to  be  equal  to 
forty  times  the  thickness  of  the  plate,  and  the  depth  will  be  ten  times  this  thickness  ; 
the  flat  edge  to  be  joined  to  the  cavity  by  a  curve  the  radius  of  which  is  not  to  be 
greater  than  the  thickness  of  the  plate.     Moreover,  plates  more  than  .197  inch  will  be 
stamped  with  a  flat-bottomed  depression  with  square  angles  and  straight  sides,  the 
diameter  of  the  bottom  to  be  thirty  times  the  thickness  of  the  plate,  and  the  depth  ten 
times  the  same  thickness.     The  bottom  of  this  cavity  will  be  pierced  with  a  round  hole, 
with  the  metal  forced  perpendicularly  beyond  the  bottom  of  the  recess ;  the  diameter 
of  the  hole  to  be  twenty  times  the  thickness  of  the  plate,  and  the  height  of  the  sides 
five  times  the  same  thickness.     All  the  corners  will  be  rounded  with  a  curve  not  of 
greater  radius  than  the  thickness  of  the  plate.     The  pieces  thus  tested,  with  every  pre- 
caution which  the  working  of  steel  requires,  must  show  no  signs  of  yielding  or  cracking, 
even  when  cooled  in  a  brisk  current  of  air. 

"  Tempering  tests :  For  these  tests  bars  10.24  inches  long  by  1.58  inches  wide  will  be 
cut  from  the  plate  longitudinally  as  well  as  transversely.  These  strips  will  be  heated 
uniformly  to  a  slightly  dull  cherry-red,  and  then  tempered  in  water  at  a  temperature  of 
82°  Fahr.  Thus  treated  they  must  be  bent  in  the  testing-machine  to  a  curve  of  which 
the  minimum  radius  is  not  greater  than  the  thickness  of  the  bars.  These  same  bars, 
when  the  corresponding  plates  are  to  be  used  for  boilers,  will  be  bent  double  in  the 
press  without  showing  any  traces  of  fracture,  and  in  such  a  way  that  the  halves  of  the 
plate  may  be  in  contact.  The  sides  of  the  bars  thus  tested,  if  round,  can  be  squared 
up  with  a  file.  Plates  not  coming  up  to  these  tests  will  be  rejected." 

11.  Tests  for  Plate,  Beam,  Angle,  Bulb,  and  Bar  Steel  used  in  building 
Ships  for  Her  Majesty's  Navy. — Admiralty,  9th  January,  1879.     (The  same  direc- 
tions are  followed  for  steel  used  for  boiler-shells.) 

"  Strips  cut  lengthwise  or  crosswise  to  have  an  ultimate  tensile  strength  of  not  less 
than  26,  and  not  exceeding  30,  tons  per  square  inch  of  section,  with  an  elongation  of  20 
per  cent,  in  a  length  of  8  inches.  The  beam,  angle,  bulb,  and  bar  steel  to  stand  such 
forge-tests,  both  hot  and  cold,  as  may  be  sufficient,  in  the  opinion  of  the  receiving 
officer,  to  prove  soundness  of  material  and  fitness  for  the  service. 

"  Strips  cut  crosswise  or  lengthwise  1£  inches  wide,  heated  uniformly  to  a  low  cherry- 


SEC.  12.  TESTING  THE  MATERIALS.  105 

red  and  cooled  in  water  of  82°  Fahr.,  must  stand  bending  in  a  press  to  a  curve  of 
which  the  inner  radius  is  one  and  a  half  times  the  thickness  of  the  steel  tested. 

"  The  strips  are  all  to  be  cut  in  a  planing-machine,  and  to  have  the  sharp  edges  taken 
off. 

"The  ductility  of  every  plate,  beam,  angle,  etc.,  is  to  be  ascertained  by  the  applica- 
tion of  one  or  both  of  these  tests  to  the  shearings,  or  by  bending  them  cold  by  the 
hammer. 

"  All  steel  to  be  free  from  lamination  and  injurious  surface-defects. 

"  One  plate,  beam,  or  angle,  etc.,  to  be  taken  for  testing  from  every  invoice,  provided 
the  number  of  plates,  beams,  or  angles,  etc.,  does  not  exceed  fifty.  If  above  that  num- 
ber, one  for  every  additional  fifty  or  portion  of  fifty.  Steel  may  be  received  or 
rejected  without  a  trial  of  every  thickness  on  the  invoice. 

"The  pieces  of  plate,  beam,  or  angle,  etc.,  cut  out  for  testing  are  to  be  of  parallel 
width  from  end  to  end,  or  for  at  least  eight  inches  of  length. 

"  Plates  may  be  ordered  either  by  weight  per  superficial  foot  or  by  thickness.  In 
the  former  case  the  weight  named  will  always  be  the  greatest  that  will  be  allowed,  and 
a  latitude  of  5  per  cent,  below  this  will  be  allowed  for  rolling  in  plates  of  J  inch  in 
thickness  and  upwards,  and  10  per  cent,  in  thinner  plates.  When  the  plates  are 
ordered  by  thickness  their  weight  is  to  be  estimated  at  the  rate  of  40  pounds  per 
square  foot  for  plates  of  one  inch  thick,  and  in  proportion  for  plates  of  all  other  thick- 
nesses. In  this  case,  also,  the  weight  due  to  the  thickness  by  this  calculation  is  not 
to  be  exceeded,  but  the  same  latitude  as  above  will  be  allowed  below  the  weight  for 
rolling.  The  average  weight  per  foot  of  the  plates  ordered  is  to  be  ascertained  by 
weighing  not  less  than  10  tons  at  a  time  when  larger  parcels  than  10  tons  are  delivered  ; 
if  these  10  tons  exceed  the  due  weight  (calculated  as  stated  above),  or  are  more  than 
the  before-mentioned  percentage  below  it,  the  whole  may  be  rejected.  In  smaller  de- 
liveries than  10  tons  the  average  is  to  be  ascertained  by  weighing  the  whole  parcel. 
The  same  conditions  as  to  latitude  and  mode  of  ascertaining  weight  apply  also  to 
other  descriptions  of  steel  in  the  contract." 

12.  Examining  Boiler-plates.— The  method  pursued  in  the  English  dockyards 
for  examining  iron  plates  as  to  imperfections  developed  in  the  process  of  manufacture 
is  described  by  Reed  as  follows:  "When  parcels  or  lots  of  iron  plates  are  delivered 
into  the  building-yard  they  are  spread  out  and  examined  with  the  object  of  first  ascer- 
taining if  the  manufacturer's  name  and  the  brand  of  quality  are  duly  stamped  upon 
each  plate,  and  then  of  searching  for  surface-defects,  such  as  blisters,  flaws,  lamina- 
tions, or  bad  places  caused  by  dirt  or  cinders  getting  between  the  rolls  during  the 


106  STEAM  BOILERS.  CHAP.  V. 

rolling  of  the  plates,  any  one  of  which,  if  considerable,  would  cause  the  overseer  to 
reject  the  plate.  This  surface-examination  being  completed,  each  plate  is  raised  from 
the  ground,  and,  being  either  hung  by  one  edge  or  otherwise  suitably  supported,  is 
tapped  over  with  a  small  hammer.  If  it  everywhere  gives  out  a  clear,  ringing  sound 
the  plate  is  considered  to  be  solid ;  but  if  a  heavy  and  dull  sound  be  given  out  it  is 
presumed  that  the  plate  is  laminated  or  otherwise  defective.  If  this  test  is  audibly 
decisive  against  the  plate  it  is  at  once  rejected  ;  but  if  the  quality  of  the  plate  appears 
doubtful  a  further  test  is  resorted  to.  This  consists  in  supporting  the  plate  at  its  four 
corners,  strewing  the  upper  surface  with  sand,  and  lightly  tapping  over  the  under  side. 
Wherever  the  plate  is  sound  the  sand  will  be  driven  up  off  the  plate  by  each  tap  of  the 
hammer,  but  if  it  is  blistered  or  laminated  at  any  place  the  sand  will  not  there  be 
moved.  The  plates  which  the  foregoing  tests  show  to  be  satisfactory  are  next  carefully 
measured  and  weighed,  their  actual  weights  being  compared  with  those  due  to  their 
dimensions  and  specified  thickness." 

It  is  convenient  to  mark  the  plate  off  with  a  chalked  line  into  squares  of  four  or  six 
inches  to  make  sure  that  each  part  of  the  plate  is  tapped  with  the  hammer ;  a  few 
blows  in  each  square  will  be  sufficient.  Both  sides  of  the  plate  should  be  thus  tested  ; 
sometimes  a  plate  will  appear  to  be  quite  sound  on  one  side,  but  will,  nevertheless,  be 
found  defective  on  the  other  side. 

All  these  tests  may,  however,  fail  to  reveal  internal  defects,  which  may  become 
apparent  as  soon  as  the  plate  is  heated  at  the  forge,  or  perhaps  not  until  it  has  been  for 
some  time  in  use  in  the  boiler. 


CHAPTEK  VI. 

PRINCIPLES   OF  THE  STRENGTH  OF  BOILERS. 

1.  Resistance  of  Spherical  Shells  to  an  Internal  Fluid  Pressure.  —  An  elas- 
tic fluid  contained  in  a  closed  vessel  presses  each  unit  of  area  of  the  surrounding  walls 
with  equal  force.  The  resistance  offered  by  the  walls  depends  on  their  superficial  area, 
their  form,  their  thickness,  and  the  coefficient  of  resistance  of  the  material. 

The  hollow  sphere  encloses  the  largest  space  in  proportion  to  the  superficial  area  of 
its  shell,  and  all  vessels  that  are  not  spherical,  exposed  to  an  internal  fluid  pressure, 
experience  distortion  on  account  of  their  tendency  to  assume  the  spherical  form.  A 
hollow  sphere,  having  a  shell  of  uniform  thickness  composed  of  a  homogeneous  ma- 
terial, experiences  the  same  tension  at  all  sections  of  metal  formed  by  diametrical 
planes. 

The  area  of  a  diametrical  section,  S,  of  a  thin  spherical  shell  is  very  nearly  given 
by  formula  : 

S  =  27i  r  t, 

when  t  represents  the  thickness,  and 
r  —  the  inner  radius  of  the  shell, 
and  t  is  supposed  to  be  very  small  compared  with  r. 

The  whole  force,  F,  to  be  resisted  by  the  tenacity  of  section  S  is  equal  to  the  excess 
of  the  internal  fluid  pressure  per  unit  of  area  over  the  external  pressure,  into  the  area 
of  the  plane  passing  through  this  section,  or 


Assuming  that  every  portion  of  section  8  is  equally  strained  by  F,  and  designating 
by  k  the  coefficient  of  the  ultimate  tenacity  of  the  material  of  which  the  shell  is  com- 
posed, the  bursting  pressure  will  be  found  from  the  equation  :  nrtp  =  2nrtJc;  hence 

2/  1  K       rT  T 

P^-^i     M 

and  the  proper  ratio  of  the  thickness  to  the  radius  of  a  thin  hollow  sphere  is  given  by 
the  formula  : 

A  .P. 

r  ~2&' 
It  is  to  be  borne  in  mind  that  this  proportion  applies  to  all  spherical  segments. 

107 


108  STEAM  BOILERS.  CHAP.VL 

The  assumption  that  all  portions  of  the  section  S  are  equally  strained  by  an  internal 
fluid  pressure  is  not  strictly  correct,  but  comes  sufficiently  near  the  truth  in  the  case  of 
thin  shells  of  such  dimensions  as  are  generally  used  in  connection  with  steam  boilers. 
Considering  the  shell  to  be  composed  of  a  number  of  concentric  layers,  the  tension  ex- 
perienced by  each  will  decrease  with  its  distance  from  the  centre,  on  account  of  the 
different  ratios  in  which  the  surface  and  the  mass  of  a  sphere  increase  with  an  increase 
of  radius. 

2.  Resistance  of  Cylindrical  Shells  to  an  Internal  Fluid  Pressure.  —  The 
tension  produced  in  a  cylindrical  shell  by  an  internal  fluid  pressure  may  be  considered 
as  being  of  two  different  kinds  —  viz.,  first,  a  tension  acting  in  a  longitudinal  direction, 
tending  to  pull  the  ends  of  the  cylinder  apart  ;  and,  secondly,  a  tension  acting  in  a  dia- 
metrical direction,  tending  to  split  the  cylinder  from  end  to  end. 

The  force,  F,  producing  the  first-named  tension  is  represented  by  the  formula  : 

F  =  r*  rrp  / 

and  the  sectional  area,  S,  of  a  thin  shell  resisting  this  force  may  be  represented  with 
sufficient  accuracy,  as  in  the  case  of  thin  spherical  shells,  by  the  formula  : 


The  value  of  p,  when  it  becomes  the  bursting  pressure,  is  found  from  the  equation, 

r*  np  =  %nrtlc  ; 

hence  p  —-'—.     [II.  ] 

It  follows  that  the  strength  of  a  cylindrical  shell  in  resisting  a  bursting  stress  applied 
in  a  longitudinal  direction  is  the  same  as  that  of  a  spherical  shell  of  equal  radius  and 
thickness. 

To  find  the  value  of  p  which  would  split  the  cylinder  from  end  to  end,  let  the  shell 
be  considered  as  divided  lengthwise  into  rings,  of  which  the  length  is  unity.  The  force 
tending  to  rupture  such  a  ring  at  the  sections  formed  by  any  diametrical  plane  is  given 
by  formula  : 


and  the  area  of  these  sections  by 

8=2t. 


SEC.  3.  PRINCIPLES  OF  THE  STRENGTH  OF  BOILERS.  109 

The  bursting  pressure  is,  therefore,  found  from  the  equation  : 

2rp  =  2tk; 

tic 
hence  p  =  —  .    [III.] 

The  value  of  p  as  found  by  equation  [III.]  is  only  half  as  great  as  the  value  found 
by  equation  [II.]  ;  hence  the  tendency  of  a  thin  cylindrical  shell  to  split  from  end  to 
end  under  an  internal  fluid  pressure  is  twice  as  great  as  its  tendency  to  rupture  circum- 
ferentially. 

Representing  the  length  of  the  cylinder  by  I,  the  equation  between  the  total  force  F, 
acting  in  a  diametrical  direction,  and  the  resistance  of  the  sections  of  the  whole  shell 
formed  by  diametrical  planes,  assumes  the  form  : 


Since  this  equation  gives  the  same  value  for  p  as  is  given  by  formula  [III.]  for  a 
cylindrical  ring  of  which  the  length  is  unity,  it  follows  that  the  strength  of  hollow 
cylinders  exposed  to  an  internal  fluid  pressure  is  independent  of  their  length. 

Cylindrical  shells  would  always  preserve  their  true  cylindrical  form  under  an  internal 
fluid  pressure,  if  their  ends  were  not  necessarily  rigidly  attached,  and  thereby  prevented 
from  expanding  equally  with  the  rest  of  the  shell  in  proportion  to  the  elasticity  of  the 
material  with  each  increase  of  pressure  ;  on  this  account  the  middle  portion  expands 
more  freely  than  the  ends,  and  the  cylindrical  tube  has  a  tendency  to  become  barrel- 
shaped  under  such  conditions.  This  effect,  however,  is  appreciable  only  in  the  case  of 
very  soft  and  elastic  materials,  and  no  account  need  be  taken  of  it  in  the  case  of  tubes 
used  in  connection  with  boilers. 

The  foregoing  remarks  about  thick  hollow  spheres  apply  equally  to  thick  hollow 
cylinders. 

The  question  has  been  raised  whether  cylindrical  shells,  when  strained  longitudinally 
and  diametrically  at  the  same  time,  did  not  offer  a  diminished  resistance  to  rupture  in 
any  one  direction.  Direct  experiments  by  Navier  on  wrought-iron  spheres  have,  how- 
ever, proved  that  the  resistance  of  the  metal,  when  the  stress  is  applied  simultaneously 
in  all  directions,  is  the  same  as  when  the  tension  acts  in  one  direction  only. 

3.  Resistance  of  Cylindrical  Shells  to  an  External  Fluid  Pressure.  —  Thin 
hollow  cylinders  exposed  to  an  external  fluid  pressure  never  give  way  by  direct  crush- 
ing, but  by  collapsing  ;  it  may  be  assumed  that,  other  things  equal,  the  resistance  of 
ttibes  to  collapsing  is  greater  as  their  form  is  more  truly  cylindrical  and  their  shell  more 
perfectly  homogeneous. 

Fairbairn  has  deduced  the  following  formula  from  experiments  made  mostly  on  very 


110 


STEAM  BOILERS. 


CHAP.  VI. 


thin  cylindrical  tubes  of  various  lengths  and  diameters  —  viz.,  for  wrought-iron  cylin- 
drical tubes  let 

I  =  the  length, 

d  —  the  diameter,  and 

I  —  the  thickness  of  the  shell,  all  expressed  in  the  same  unit  of  measure,  and  let 
p  =  the  collapsing  pressure  in  pounds  per  unit  of  area  ;  then 

p  =  9,672,000  ^°.     [IV.] 

In  case  a  tube  is  stiffened  by  T-iron  rings  or  by  flanges,  I  represents  the  distance  be- 
tween two  such  adjacent  rings  or  flanges. 

Fairbairn  finds  that  the  collapsing  pressure  of  a  flue  of  an  elliptic  form  of  cross- 
section  is  found  approximately  by  substituting,  in  the  preceding  formula,  for  d  the 
diameter  of  the  osculating  circle  at  the  flattest  part  of  the  ellipse  —  that  is,  let  a  be  the 
greater  and  b  the  less  semi-axis  of  the  ellipse  ;  then  we  are  to  make 


In  order  to  facilitate  calculations  by  this  formula  the  2.19th  power  is  given  in  the 
following  table  for  such  mimbers  as  represent,  in  fractions  of  an  inch,  the  thicknesses  of 
boiler-plates  most  frequently  used  in  the  construction  of  boiler-flues  : 

TABLE  XX. 


a.igth  power  of  number. 

Logarithm  of  2.i9th  power. 

A 

A 
A 

.18750 
.21875 
.25000 
.28125 

•025578  + 

•°3585o  — 
•048027  + 
.062160  + 

.4078728  2 
.5544863  —  2 
.6814886  —  2 
.7935126  —  2 

A 
H 

1 
U 

.3125° 

•34375 
•375°° 
.40625 

.078293- 
.096465  + 
.116715  — 
.139078  — 

.8937215—2 

•9843715—2 
.0671285  I, 

•M32575   "I 

A 
H 
i 
H 

-4375° 
.46875 
.50000 
•S3I2S 

•163584  + 
.190266  + 
.219151  + 
.250267  + 

.2137420  I 
.2793614—  I 

•3407443  —  I 
.3984046  —  I 

A 

1 
H 

1 

•56250 
.62500 

.68750 
.75000 

.283641  - 

•357254  + 
.440177  — 

•532579  + 

•4527683—  I 
•5529772—! 
.6436272  —  1 
.7263842—  I 

In  an  article  in  the  Annales  du  Genie  civil,  March,  1879,  on  the  "  Resistance  of 


SET.  3.  PRINCIPLES  OF  THE  STRENGTH  OP  BOILERS.  Ill 

Tubes  subjected  to  an  External  Pressure,"  by  Theodore  Belpaire,  an  attempt  has  been 
made  to  deduce  a  new  formula  for  the  collapsing  strength  of  tubes.  The  following  is  a 
brief  synopsis  of  the  contents  of  this  paper : 

A  tube  having  a  perfectly  cylindrical  form  and  a  circular  cross-section,  and  being 
made  of  a  homogeneous  material,  would  remain  cylindrical  under  increasing  pressures 
till  the  material  gave  way  by  crushing.  But  the  circular  cross-section  is  a  form  of  un- 
stable equilibrium  for  resisting  external  pressure,  because  a  slight  alteration  of  shape 
suffices  to  destroy  the  equilibrium  under  sufficiently  great  pressures.  Want  of  homo- 
geneity of  the  material  has  likewise  a  great  influence  on  the  resistance.  It  would  be 
imprudent  to  rely  under  such  circumstances  upon  the  increase  of  resistance  due  to  the 
homogeneity  of  the  material  and  to  the  circular  form,  since  it  is  impossible  to  know  in 
advance  to  what  extent  they  will  be  realized  in  construction.  Fairbairn's  formula 
represents  the  results  of  experiments  where  this  increase  of  resistance  obtained  to  a 
greater  or  less  extent,  and  for  this  reason  it  does  not  appear  to  be  reliable  for  determin- 
ing the  dimensions  which  should  be  given  to  internal  flues.  Such  flues  derive  their 
strength  mainly  from  the  fastening  of  their  ends,  which  may  be  considered  as  absolutely 
rigid,  and  sometimes  from  rigid  rings  by  means  of  which  the  intermediate  sections  of 
the  flues  are  joined  together.  The  collapsing  of  a  cylinder  is  always  preceded  by  dis- 
tortion ;  it  is  evident  that  collapse  cannot  take  place  when  this  distortion  is  not  allowed 
to  exceed  a  certain  limit  and  the  material  is  not  unduly  strained. 

The  writer  then  considers  the  case  of  a  tube  with  ends  rigidly  fixed,  and  supposes 
that  under  an  external  pressure  it  changes  its  form  in  such  a  manner  that  its  generatrix 
becomes  the  arc  of  a  circle,  the  centre  of  which  lies  on  a  perpendicular  erected  in  the 
centre  of  the  generatrix  ;  and,  neglecting  the  elastic  forces  due  to  flexure  or  elongation 
of  the  fibres — which  are  very  small  as  long  as  the  curvature  is  slight — he  investigates 
the  shearing  stresses  ;  these  attain  their  greatest  value  at  the  fixed  ends. 

Calling  S  the  greatest  shearing  stress, 

p  the  pressure  in  pounds  per  square  inch, 
t  the  thickness  of  the  tube  in  inches, 
L  the  length  of  the  tube  in  inches, 

he  deduces  the  following  approximate  formula  for  the  external  pressure  which  a  given 
tube  can  bear  with  a  degree  of  safety  depending  on  the  value  attributed  to  S— viz. : 

^  t  *b  rTTT   T 

p=   L  •     [>!•] 

The  writer  deduces  then  a  general  value  S  from  two  experiments  made  by  Fairbairn 
with  elliptical  tubes,  because  the  uncertain  and  variable  elements  of  strength  due  to  the 


112 


STEAM  BOILERS. 


CHAP.  VI. 


cylindrical  form  and  to  homogeneity  of  the  material  do  not  enter  here.     When  the 
factor  of  safety  in  the  foregoing  equation  is  to  be  four,  the  value  of  S  becomes 

8=  428,394  ^  -  7,111,550  (^j  ; 

where  t  is  the  thickness  and  D  the  diameter,  both  expressed  in  inches. 

Since  externally-pressed  tubes  always  derive  a  large  increase  of  strength  from  their 
circular  form,  a  factor  of  safety  of  four  is  considered  sufficient  in  using  these  formulas. 

Applying  these  formulas  to  34  cases  where  tubes  collapsed  either  in  an  experimental 
apparatus  or  during  actual  use  in  a  steam  boiler,  the  factor  is  found  to  vary  actually 
from  4.2  to  16.8.  With  reference  to  those  cases  where  the  factor  of  safety  exceeded 
four  greatly,  the  writer  claims  that  the  high  pressures  necessary  to  produce  collapse 
indicate  merely  the  great  increase  of  strength  derived  in  the  particular  instances  from 
the  uncertain  element  of  circular  form. 

A  greater  number  of  experiments  are  required  from  which  to  deduce  an  expression 
for  8,  so  that  the  influence  of  thickness  and  diameter  of  the  tube,  and  of  the  eccentricity 
of  its  elliptical  cross-section,  on  the  value  of  $  may  be  fully  determined. 

For  the  purpose  of  applying  the  foregoing  formulas  in  practice  the  following  table 

has  been  calculated,  giving  the  values  of  £  for  different  values  of  ^-  and  for  different 

factors  of  safety : 

TABLE  XXI. 


Values  of 

Values  of  ^  for  a  factor  of  safety  of 

Values  of 

Values  of  -S1  for  a  factor  of  safety  of 

t 

t 

D 

4 

5 

6 

D 

4 

5 

6 

0.003 

1221 

1526 

1832 

O.OI2 

4117 

5^6 

6175 

0.004 

l6oO 

2OOO 

2400 

0.013 

4367 

5459 

655° 

0.005 

1964 

24S5 

2946 

0.014 

4604 

5755 

6906 

0.006 

23M 

2892 

3471 

0.015 

4826 

6032 

7239 

O.OO7 

2650 

3312 

3975 

0.016 

5°34 

6292 

755i 

O.OO8 

2972 

3715 

445s 

0.017 

5227 

6534 

7840 

O.OOp 

3280 

4100 

4920 

0.018 

5407 

6759 

8no 

O.OIO 

3573 

4466 

536o 

0.019 

5572 

6965 

8358 

O.OII 

3852 

48IS 

5778 

O.O2O 

5723 

7i54 

8585 

Professor  Grashof  has  derived  from  Fairbairn's  experiments  the  following  empirical 

formula — viz. : 

ft.tn 

p  =  1,057,180     i0.B8. 


SEC.  4. 


PRINCIPLES   OP   THE  STRENGTH  OP  BOILERS. 


113 


In  which  d  =  diameter  of  the  tube  in  inches ; 
I  =  length  of  the  tube  in  inches  ; 
t  =  thickness  of  the  tube  in  inches  ; 
p  =  pressure  in  pounds  per  square  inch. 

4.  Experiments  made  on  the  Resistance  of  Cylindrical  Flues  to  an  Ex- 
ternal Fluid  Pressure.— In  the  year  1874  experiments  were  made  at  the  Washington 
Navy- Yard  to  determine  the  resistance  of  large  cylindrical  boiler-flues  to  collapse.  The 
apparatus  used  for  this  purpose  is  represented  in  figure  5. 

Fig.  5. 


i  — 


4- 


It  consisted  of  a  cylindrical  shell  of  63  inches  diameter,  constructed  of  boiler-iron 
f  inch  thick.  A  cylindrical  flue,  77|  inches  long  and  54  inches  in  inside  diameter,  was 
securely  riveted  to  flanges  within  this  shell.  This  inner  cylindrical  flue  was  con- 
structed of  i-inch  boiler-iron,  and  consisted  of  two  rings  connected  by  an  interior  butt- 
strap  7f  inches  wide  and  J  inch  thick.  Each  ring  was  formed  of  two  plates  with  butt- 
joints,  the  butt-straps,  7|  inches  wide  and  £  inch  thick,  being  placed  on  the  inside. 


114 


STEAM  BOILERS. 


CHAP.  VI. 


The  longitudinal  seams  of  the  rings  broke  joint  as  shown  in  the  drawing.  All  seams 
were  double-riveted  .and  carefully  calked.  The  unsupported  length  of  the  internal  flue 
(measured  between  the  inner  edges  of  rivet-holes)  was  71J  inches.  A  2f-inch  pipe 
screwed  into  the  outer  shell  connected  with  a  force-pump,  by  means  of  which  a  hydro- 
static pressure  was  produced  during  the  trials  within  the  annular  space  formed  by  the 
two  cylinders.  Carefully-tested  spring-gauges  indicated  the  pressure.  One  of  the 
rings  of  the  inner  shell  collapsed  under  a  pressure  applied  to  try  the  tightness  of  the 
joints  and  rivets,  the  two  gauges  used  indicating  a  pressure  of  100  Ibs.  and  110  Ibs.  re- 
spectively. The  mean  of  these  two  readings  was  probably  the  true  pressure,  as,  on  com- 
parison with  a  standard  gauge,  the  one  gauge  was  found  to  indicate  less  and  the  other 
more  than  the  true  reading  near  that  pressure.  The  bulged  portion  of  the  shell  of  the 
flue  was  pressed  out  and  shored  up  from  the  opposite  side  of  the  flue,  and  the  pressure 
was  again  applied.  This  time  collapse  took  place  in  the  other  ring ;  then  the  opera- 
tion of  forcing  out  and  shoring  up  was  repeated.  It  is  evident  that  by  this  shoring  up 
the  flue  became  stiffer  each  time,  and  the  results  of  the  successive  trials  indicate  this. 
The  following  are  the  results  of  the  tests  made  with  this  flue  : 

1st  collapsed  in  testing  joints  and  rivets,  at       105  Ibs. 
2d  with  one  bulge  shored  up,  at        120   " 

3d  "        with  two  bulges  shored  up,  at      148   " 

4th         "        with  three  bulges  shored  up,  at    155   " 
5th  with  four  bulges  shored  up,  at     186   " 

Careful  measurement  after  construction  had  revealed  the  fact  that  the  flue  was  slightly 
oval,  the  larger  diameter  being  54^  inches  and  the  smaller  diameter  53|  inches ;  and 
on  removing  the  shell  and  gauging  the  sheets  composing  the  flue,  the  one  which  had 
collapsed  first  was  found  to  be  slightly  less  in  thickness  than  J  inch. 

Another  flue  of  J-inch  boiler-iron  was  made,  care  being  taken  to  gauge  the  sheets 
accurately  before  fitting  them.  This  flue  consisted  likewise  of  two  courses,  38  inches 
and  39  inches  long  respectively,  but  they  were  connected  by  flanges,  with  a  ring  H  inch 
thick  between  them  (see  figure  6). 


Fig.  6 


This  flue  was  found  to  be  perfectly  cylindrical,  having  an  internal  diameter  of  exactly 
54  inches. 


SEC.  5.  PRINCIPLES  OP  THE  STRENGTH  OP  BOILERS.  115 

Three  spring-gauges,  that  had  been  carefully  compared  with  a  standard  gauge, 
were  used  to  measure  the  pressure.  After  the  first  trial  the  bulged  portion  of  one 
course  was  shored  up  as  before  described,  and  a  second  trial  made,  when  the  other 
course  collapsed. 

Fiist  trial.          Second  trial. 

Ashcroft's  gauge  .....................................  132  Ibs.     130  Ibs. 

Post's  gauge  .........................................   134   "       131   " 

Utica  gauge  ..........................................  134   "       131    " 

Applying  to  the  first  experimental  flue  Fairbairn's  formula,  modified  for  elliptical 

/  ».'t     i 

tubes,   viz.,  p  —  9,672,000  -i—  -,  -f,  we  get  for  the  collapsing  pressure  p  =  118.42  Ibs. 

<&  a     l 

This  result  shows  a  close  agreement  with  the  first  two  results  of  the  experiment,  when 
the  reduced  thickness  of  one  of  the  sheets  is  taken  into  consideration. 

The  collapsing  pressure  of  the  second  flue  should  have  been  nearly  240  Ibs.  according 
to  Fairbairn's  formula,  and  225  Ibs.  according  to  Grashof  's  formula. 

Belpaire's  formula  gives  for  the  collapsing  pressure  of  the  second  flue  101.2  Ibs.  per 
square  inch  ;  the  actual  higher  collapsing  pressure  indicating  the  increase  of  strength 
due  to  the  circular  form. 

5.  Strength  of  Flat  Plates  —  The  theory  of  flexure  for  loaded  flat  plates  leads  to 
very  complicated  expressions.  The  following  approximate  method  is  employed  by 
Weisbach  ('  Manual  of  the  Mechanics  of  Engineering,'  vol.  ii.)  for  finding  the  thickness 
of  such  plates  : 

Let  m  —  the  length,  and  n  =  the  width  of  a  rectangular  flat  plate  secured  at  the  cir- 
cumference to  a  solid  frame  or  by  a  row  of  rivets,  and  p  =  the  pressure  which  it  has  to 
sustain  per  unit  of  surface.  Let  us  imagine  this  sheet  to  be  cut  into  parallel  strips  in 
the  direction  of  the  length,  the  ends  of  which  are  secured  to  the  frame  ;  and  let  us 
assume  that  the  portion  p,  of  the  pressure  p  causes  the  tension  of  these  strips  ;  then,  if 
we  indicate  the  breadth  of  each  strip  by  b,  the  thickness  by  t,  and  the  coefficient  of  re- 
sistance to  rupture  by  I;  we  have  the  equation  : 


m 
or  mt= 


hence  t  =  *,Vj       [VII.] 

-   /*' 

If,  on  the  other  hand,  we  imagine  the  plate  cut  up  into  similar  strips  in  the  direction 


116  STEAM  BOILERS.  CHAP.  VI. 

of  its  breadth,  and  assume  that  the  tension  of  these  strips  is  caused  by  the  pressure 
pt  =  p  —  pl}  we  find  in  the  same  manner 


*???*  ¥)  *7?*  T) 

As  the  deflection  in  the  first  case  decreases  as  —  if-1,  and  in  the  other  case  as      .,    ,  and 
as  it  is  as  great  in  the  one  case  as  in  the  other,  we  can  put 


hence  Pi  =  —f  Pi  and  p  =  p 

4 

consequently  p,  =     4  jf. . 


By  introducing  these  values  of  pt  and  p,  into  equations  [VII.]  and  [VII.  a]  we  get  for 
the  thickness  of  the  plate  in  the  first  case 


, 

• 

and  in  the  second  case 


p 


If  n  >  m,  we  must  find  the  thickness  of  the  plate  according  to  formula  [VIII.]  ;   if 
m  >  n,  we  must  use  formula  [VIII.  a]. 

For  square  sheets  we  have  m  =  n,  therefore 


*  =  [IX-] 

The  following  formulas  are  given  by  Rankine  for  calculating  the  strength  of  un- 
stayed  flat  surfaces  secured  at  the  edges,  in  which  p,  t,  r,  and  Tc  denote  the  same  quan- 
tities as  in  sections  1  and  2  of  the  present  chapter  : 

m  is  the  length  of  a  rectangular  plate,  or  the  side  of  a  square  plate,  in  inches  ; 

n  is  the  breadth  of  a  rectangular  plate  in  inches  ; 

m  being  greater  than  n  in  the  case  of  rectangular  plates  : 


Flat  circular  plates  :  P  =       i    [X.]  t  =  r\\    [X.a] 


Flat  rectangular            4P  (m'  +  Qfr.  -,        z-866m'X7V        P         •     rXT  a\ 

plates:                             Sm'xn*  Y  F(^T^)' 

Flat  square  plates  :                p  =  i|£-*;  [XII.]                          t  =  .612  m  y  -£;     [Xlla.] 

3  Tfl  K 


SBC.  6.  PRINCIPLES  OP  THE  STRENGTH  OP  BOILERS.  117 

Comparing  the  thickness  required  for  a  flat  circular  plate,  as  given  by  formula  [Xa.], 
with  the  thickness  of  a  cylindrical  shell  of  equal  radius  and  of  equal  strength,  as  given 

by  formula  [III.],  section  2  of  the  present  chapter,  viz.,  T  =  ^-,  we  find 


For  a  boiler  3  feet  in  diameter  and  having  a  cylindrical  shell  f  inch  thick,  single- 
riveted,  the  solid  unstayed  flat  end-plate  would  have  to  be  about  2  inches  thick  to 
make  it  as  strong  as  the  cylindrical  shell.  It  is,  however,  impracticable  to  use  such 
heavy  plates  in  boiler-construction  ;  extensive  flat  surfaces  of  boilers  are  therefore  sup- 
ported by  stays  or  stiffened  by  various  contrivances,  so  that  they  may  be  formed  of 
relatively  thin  plates.  Various  methods  of  staying  flat  surfaces  will  be  described,  and 
rules  for  proportioning  braces  will  be  given,  in  chapter  x. 

Experiments  on  the  strength  of  flat  ends  of  cylindrical  vessels,  described  by  Robert 
Wilson  in  Engineering,  September  28,  1877,  indicate  that  the  actual  breaking  strength 
of  flat  plates  is  much  greater  than  that  given  by  the  above  formulae,  and  that  the  flat 
end-plates  of  boilers  receive  a  great  access  of  strength  and  stiffness  by  flanging  their 
edges.  But  flat  plates  begin  to  bulge  out  with  very  low  pressures,  and  the  springing  of 
the  plates  as  the  pressure  is  alternately  applied  and  relieved  destroys  them  inevitably 
in  the  course  of  time  by  grooving  or  channelling. 

The  stiffness  of  plates  is  greatly  increased  by  buckling  ;  and  when  the  surfaces  are 
not  too  large  buckled  plates  are  sometimes  used  in  boilers  instead  of  stayed  flat  plates. 
Rankine  gives  the  following  rule  for  calculating  "the  load,  uniformly  distributed  over  a 
buckled  plate,  which  will  crush  it,  the  plate  being  square  and  fastened  all  around  the 
edges  :  Multiply  the  depth  to  which  the  plate  is  bucTcled  by  the  square  of  the  thickness, 
both  in  inches,  and  by  165  ;  the  product  will  be  the  crushing  load  in  tons,  nearly.  Cen- 
tral load  which  crushes  a  buckled  plate  about  one-third  of  uniformly-distributed  load." 

6.  Strains  on  Braces  and  their  Attachments.—  When  a  boiler  is  composed  of 
thin,  flat  plates  offering  little  resistance  to  bending,  it  may  be  assumed  without  serious 
error  that  the  stress  experienced  by  a  brace  is  the  resultant  of  the  whole  pressure  act- 
ing perpendicularly  to  the  portion  of  the  plate  supported  by  the  brace.  When  the 
plates  are  increased  in  thickness,  or  are  strengthened  by  angle  or  T-irons,  their  increased 
resistance  to  bending  causes  a  corresponding  diminution  of  the  stress  on  the  braces. 

A  brace  standing  perpendicular  to  a  thin,  flat  plate  experiences  a  tensile  stress  equal 


118 


STEAM  BOILERS. 


CHAP.  VI. 


to  the  total  pressure  borne  by  the  supported  surface.     This  may  be  expressed  by  the 
equation  : 


when  S—  the  area  of  the  supported  surface  in  square  inches  ; 
p  —  the  steam-pressure  in  pounds  per  square  inch  ; 
and  T  =  the  total  tension,  in  pounds,  of  the  brace. 

The  tension  of  an  oblique  brace  is  equal  to  the  tension  which  a  perpendicular  brace 
supporting  the  same  surface  would  experience,  divided  by  the  cosine  of  the  angle  which 
the  oblique  brace  forms  with  a  perpendicular  to  the  supported  surface  (see  figure  7),  or 

Tl  =     p8    .     [XIV.] 
cos.  oc 

When  T  '  is  resolved  into  a  pair  of  rectangular  components  acting  respectively  in  a 


Fig.  7. 


perpendicular  and  parallel  direction  to  the  supported  surface, 

the  latter  component  is  equal  to 

T1  sin.  a  =  p  S  tang,  a,     [XIV. a] 

and  produces  a  bending  strain  on  the  brace  when  its  ends  are 

rigidly  fastened  so  that  its  angular  position  is  fixed.  When 
the  ends  of  the  oblique  brace  are  attached  by  movable  joints — for  instance,  by  an  eye 
and  pin — offering  little  or  no  resistance  to  a  change  in  the  angular  position  of  the  brace, 
the  component  T1  sin.  a  exerts  a  thrust  on  the  plate  to  which  the  brace  is  attached, 
tending  to  produce  buckling. 

In  order  to  investigate  the  various  strains  obtaining  in  a  system  of  oblique  bracing, 
and  the  conditions  required  for  the  establishment  of  equilibrium,  the  braces  shown  on 
Plate  (VII.),  which  tie  the  top  of  the  boiler  to  the 
sides  of  the  tube-boxes,  are  taken  as  an  example. 
The  top  of  the  boiler  is  stiffened  by  T-irons,  to 
which  the  branch-braces  are  attached ;  the  latter 
being  spaced  so  that  each  one  supports  an  equal 
area  of  plate.  The  points  of  attachment,  A,  B,  and 
D,  are  given,  and  the  main  brace,  E  D,  is  to  have 
such  a  direction  that  the  resultant  of  the  stresses 
on  E  A  and  B  E  does  not  produce  flexure,  but 
simply  tension  on  E  D. 

Let  P  P  represent  the  resultants  of  the  forces 
acting  at  right  angles  to  the  supported  plate  at  the  point  of  attachment  of  the  oblique 
branches,  A  E  and  B  E,  to  the  T-iron  ; 


SBC.  7. 


PRINCIPLES  OP  THE  STRENGTH  OF  BOILEB8. 


119 


R  =  the  corresponding  stress  on  the  brace  D  E  ;  and 
T,  r'  the  stresses  on  A  E  and  B  E  respectively.     (See  figure  8.) 
In  order  to  balance  the  equal  forces  P  P,  the  components  of  r  and  r',  normal  to 
A  B,  must  each  be  equal  in  amount  and  opposite  in  direction  to  P  P  ;  this  condition  is 

P  P 


fulfilled  when  r  — 


and  r'  = 


The  components  of  r  and  r',  pax- 


cos.  A  JSf"  ~cos.BEF' 

allel  to  A  B   and  equal  to  P  x  tan.  A  E  F  and  P  x  tan.  B  E  F  respectively,  are 
resisted  by  the  stiffness  of  the  T-iron. 

The  forces  r  and  r'  being  each  resolved  into  two  rectangular  components,  respec- 
tively parallel  and  normal  to  E  D,  the  sum  of  the  former  gives  the  tension  of  the  brace 
E  D,  while  the  normal  components  L  E  and  K  E  tend  to  deflect  E  D.  Equilibrium 
requires  that  these  normal  components  of  the  forces  r  and  r'  should  be  equal  in  amount 
and  opposite  in  direction,  so  that  they  balance  each  other ;  and  that  the  component  of 

2P 


the  tension  R,  normal  to  A  B,  should  be  equal  to  2  P,  or  R  — 


These  con- 


cos.  FEC" 

ditions  are  fulfilled  when  the  prolongation  of  E  D  intersects  the  line  A  B  at  its  centre, 
or  when  A  C  =  B  C.  The  following  proportion  then  exists  between  the  force  P  and  the 
tension  of  the  main  brace  and  of  the  branches — P  :H:r  :  r'  :  :EF:2EC:AE:BE. 

When  the  direction  of  E  D  is  normal  to  A  B  the  foregoing  conditions  give  the  equa- 
tions R  =  2  P,  and  r  —  r'. 

7.  Strains  on  Circular  Arcs. — An  internal  normal  pressure  on  any  point  of  an 
arc  produces  at  such  a  point  a  tension  acting  in  a  tangential  direction,  equal  to  the  nor- 
mal pressure  multiplied  by  the  radius  of  curvature  at  the  point  in  question ;  conse- 
quently, when  the  flat  sides  of  the  shell  of  a  boiler  are  connected  by  a  circular  arch — 


FFg.  9. 


forming  tangential  planes  to  the  cylindrical 
surface — they  experience,  per  unit  of  length, 
a  tension  equal  to  the  product  of  the  pressure 
per  unit  of  area  and  the  radius  of  the  arch. 

When  the  shell  is  formed  by  combining 
several  cylindrical  arches,  as  in  "Emery's 
Connected- Arc  Boiler"  (see  figure  92),  the 
strains  on  the  braces  which  keep  the  system 
in  equilibrium  under  pressure  may  be  found  in 
the  following  manner : 

If  the  semicircle  M  P  represents  the  cross- 


section  of  a  cylindrical  arch  subjected  to  internal  fluid  pressure  (see  figure  9)  we  may 


120 


STEAM  BOILERS. 


CHAP.  VL 


represent  the  resultant  tangential  force  at  any  point  of  the  circumference — M,,  for 
instance — by  a  tangent  line  M,  V  made  equal  to  the  radius  Ma  O.  Resolving  this  tan- 
gential force  M,  V  into  two  rectangular  components,  represented  in  magnitude  and 
direction  by  the  lines  V  W  and  M3  W,  respectively  parallel  and  perpendicular  to  the 
diameter  M  P,  we  find  that,  since  the  triangle  M,  V  W  is  similar  and  equal  to  the 
triangle  O  M,  N,,  line  M,  N,  (equal  to  the  sine  of  arc  M  M,)  and  line  O  N,  (equal  to  the 
cosine  of  arc  M  M,)  represent  the  intensity  of  the  rectangular  forces  which  balance  the 
tangential  force  at  the  point  M5,  each  of  said  rectangular  components  acting,  however, 
in  the  direction  of  the  other. 

"If  we  consider  M  P  and  M8  O  rectangular  co-ordinate  axes,  passing  through  the 
centre  O  of  the  circle,  then  the  two  forces  required  to  hold  in  equilibrium  the  end  of 
any  arc  forming  part  of  the  quadrant  M  M8  will  be  measured  respectively  by  the  pro- 
jections of  the  arc  and  of  its  complement  upon  the  co-ordinate  axes,  and  equal  the 
length  of  such  projections  multiplied  by  the  pressure  per  superficial  unit.  For  instance, 
the  horizontal  component  required  to  balance  the  tangential  force  at  Ma  is  measured  by 
M.,  N,  =  sin.  M,  O  M  =  O  Ta,  or  the  projection  of  the  arc  Ma  M  on  axis  M8  O,  and  the 
strain  equals  O  T,  multiplied  by  the  pressure  per  superficial  unit.  The  vertical  compo- 
nent is  similarly  measured  by  N,  O  =  cos.  M,  O  M,  or  the  projection  of  the  arc  M2  Mft, 
which  is  the  complement  of  arc  M  M2,  on  the  axis  M  P ;  and  the  strain  equals  N,  O 
multiplied  by  the  pressure  per  superficial  unit." 

If  figure  10  represents  a  section  of  a  boiler  consist- 
ing of  a  series  of  connected  circular  arcs  of  eqiial 
radii — the  centres,  O,,  O,,  O,,  and  O4,  of  the  circles  all 
being  located  in  the  horizontal  line  x  y — then,  accord- 
ing to  the  foregoing  demonstration,  the  horizontal 
component  of  the  tangential  force  at  U  due  to  the 
pressure  on  arc  x  U  may  be  represented  by  U  Y,  and 
the  horizontal  component  of  the  tangential  force  at  the  same  point  U,  due  to  the  pres- 
sure on  arc  U  Ua,  may  likewise  be  represented  by  U  Y,  but  it  acts  in  the  opposite  direc- 
tion ;  consequently  these  two  horizontal  components  of  the  tangential  forces  of  the 
adjoining  arcs  balance  each  other.  The  vertical  components  of  the  tangential  forces 
acting  at  the  same  point  may  be  represented  by  the  horizontal  projections  of  the 
arcs  W  U  and  U  W5 — viz.,  O,  Y  and  Y  0, — both  acting  in  the  same  direction.  The 
same  reasoning  applies  to  the  points  U,,  U,,  V,  V,,  V,.  Supposing  the  above  figure 
to  be  symmetrical  with  regard  to  the  axis  x  y,  the  system  of  connected  arcs  will  be 
held  in  equilibrium  by  the  vertical  ties  U  V,  U,  V,,  U,  V,,  each  one  of  which  has  to 


Fig.  10. 


SEC.  7. 


PRINCIPLES  OF  THE  STRENGTH  OP  BOILERS. 


121 


sustain  a  pull,  for  each  unit  of  length  supported,  equal  to  the  pressure  per  unit  of 
area  multiplied  by  the  distance  between  the  centres  O,  O,,  O,  0,,  and  O,  O,  respec- 
tively. 


Fig.  11. 


The  same  rule  applies  to  the  cases  illustrated  in  figures  11,  12,  where  the  connected 
arcs  have  different  radii,  but  have  their  centres  on  the  same  horizontal  line  x  y. 

When  the  centres  of  the  connected  arcs  do  not  lie  on  the  same  horizontal  line  x  y, 
as  in  figures  13,  14,  the  strains  on  the  vertical  ties  are  measured  as  before  by  the  hori- 
zontal distance  between  the  centres — viz.,  O  Y  4-  Y6  O,.  But  in  figure  13  the  horizontal 
strain  of  the  arc  W  U  is  measured  by  U  Y,  while  that  of  the  arc  U  U,  is  measured  by 


Fig.  14. 


U  Ys,  less  than  U  Y  ;  hence  the  arc  W  U  tends  to  straighten  the  arc  U  U,  by  a  force 
measured  by  U  Y  -  -  U  Y,  =  Y  Y, ;  this  action  has  to  be  prevented  by  a  tie-rod,  U  U,. 

In  figure  14  the  horizontal  strains  of  the  middle  arc  U  U,  being  greater  than  those 
of  the  outer  arcs  by  an  amount  Y  Y6,  the  outer  arcs  will  fail  of  themselves  to  furnish 
sufficient  support,  and  a  strut  must  be  placed  from  U  to  U,,  which  has  to  sustain  a  com- 
pressive  strain  measured  by  Y  Y6.  (See  paper  on  '  Connected- Arc  Marine  Boilers,'  by 
C.  E.  Emery,  read  before  American  Society  of  Civil  Engineers,  December,  1876.) 


CHAPTER  VII. 

DESIGN,    DRAWINGS,    AND   SPECIFICATIONS. 

1.  General  Considerations  governing  the  Design  of  Marine  Boilers. — The 

designing  of  a  marine  boiler,  especially  for  a  war-vessel,  involves  the  fulfilment  of 
many  conditions  which  are  to  some  extent  antagonistic  ;  hence  compromises  have  to  be 
made,  and  some  advantages  with  regard  to  economic  and  potential  efficiency  have  to  be 
sacrificed  to  other  essential  conditions.  The  principal  conditions  to  be  satisfied  in  the 
design  of  a  boiler  may  be  considered  under  the  following  heads  :  (1)  The  boiler  must 
be  able  to  furnish  the  power  required  ;  (2)  its  parts  must  be  proportioned  and  arranged 
with  regard  to  economic  efficiency,  durability,  and  economy  in  construction  ;  (3)  every 
part  of  the  boiler  must  possess  the  necessary  strength. 

The  principal  restriction  imposed  on  the  designer  of  marine  boilers  of  a  given  power 
is  the  limitation  with  regard  to  the  weight  of,  and  the  space  allotted  to,  the  boilers 
proper  and  their  attachments,  the  fire-room  and  the  fuel.  In  a  man-of-war,  where  it  is 
especially  important  that  all  parts  of  the  machinery  should  be  placed  as  low  as  possi- 
ble in  the  vessel,  it  is  generally  stipulated  that  no  part  connected  with  the  steam-space 
of  the  boilers  shall  reach  above  the  water-line.  In  marine  boilers  of  the  ordinary  type, 
having  the  tubes  or  flues  arranged  over  the  furnaces,  the  area  of  the  grate-surface  is 
the  principal  element  which  determines  the  space  occupied  by  the  boilers  in  the  length 
and  breadth  of  the  vessel.  It  is,  therefore,  convenient  to  determine  the  grate-surface 
in  the  first  place,  and  to  proportion  and  arrange  the  other  parts  of  the  boiler  afterward 
according  to  the  conditions  imposed. 

The  width  of  the  fire-room  must  exceed  the  length  of  the  grate  by  at  least  two  feet, 
in  order  that  the  tools  used  in  the  management  of  the  fires  may  be  manipulated  with- 
out hindrance.  In  general  the  most  economical  disposition  of  the  room  is  made  by 
arranging  the  boilers  in  pairs,  facing  each  other,  with  the  fire-room  between  them. 

2.  Boiler-power. — The  power  of  a  boiler  is  measured  by  the  weight  of  steam  which 
it  can  generate  in  a  unit  of  time.     It  is  customary  to  measure  the  relative  evaporative 
efficiency  of  boilers  by  the  number  of  pounds  of  water  of  212°  that  can  be  evaporated 
under  atmospheric  pressure  in  a  unit  of  time ;  but  the  actual  power  of  a  boiler  must 
be  calculated  from  the  weight  of  steam  of  the  working  pressure  that  can  be  generated 

128 


SEC.  3.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  123 

in  a  unit  of  time  from  the  feed- water  as  delivered  into  the  boiler.  The  average  tem- 
perature of  the  feed-water  of  marine  boilers  may  be  taken  as  115°  when  no  heaters  are 
used. 

The  number  of  heat-units  that  can  be  made  available  and  the  weight  of  water  of  a 
given  temperature  that  can  be  evaporated  under  a  given  pressure  in  a  unit  of  time  in  a 
given  type  of  boiler,  under  different  conditions  with  regard  to  fuel,  draught,  rate  of 
combustion,  and  proportion  of  heating-surfaces,  are  to  be  calculated  according  to  the 
laws  governing  combustion  and  evaporation,  and  from  the  experimental  data  given  in 
chapters  ii.  and  iii.  of  this  treatise. 

Marine  engines  consume  from  20  to  30  Ibs.  of  steam  per  indicated  horse-power  per 
hour,  the  latter  quantity  being  consumed  by  engines  using  saturated  steam  of  about 
35  Ibs.  pressure  above  the  atmosphere,  with  a  moderate  rate  of  expansion,  the  cylinders 
having  no  steam-jacket ;  the  former  quantity  is  required  for  the  best  types  of  engine 
using  dry  steam  of  from  60  to  80  Ibs.  pressure  above  the  atmosphere,  working  with  a 
high  rate  of  expansion,  the  cylinders  being  provided  with  a  steam-jacket. .  A  marine 
boiler  of  ordinary  type  and  proportions,  using  natural  chimney-draught,  produces 
under  these  conditions  with  anthracite  coal  from  3.5  to  5.5  indicated  horse-powers  per 
square  foot  of  grate,  with  a  free-burning,  semi-bituminous  coal  from  4.5  to  7.5  indicated 
horse-powers  per  square  foot  of  grate.  With  forced  draught  as  many  as  10  indicated 
horse-powers  per  square  foot  of  grate  have  been  developed  by  several  large  English 
naval  vessels  of  recent  construction,  during  their  full-power  trial  for  six  consecutive 
hours  at  sea,  by  using  from  25  to  30  Ibs.  of  a  carefully-selected  free-burning  coal  per 
square  foot  of  grate  per  hour. 

In  a  large  number  of  locomotive  boilers,  containing  from  52  to  90  square  feet  of 
heating-surface  to  each  square  foot  of  grate-surface,  the  rate  of  combustion  increasing 
from  43  to  126  Ibs.  of  coke  with  the  above  proportions  of  heating-surface,  the  average 
evaporation  was,  according  to  D.  K.  Clark,  9  Ibs.  of  water,  at  the  ordinary  tempera- 
tures and  pressures,  per  pound  of  coke. 

3.  Various  Types  of  Marine  Boilers. — Various  types  of  marine  boilers  are  dis- 
tinguished either  by  the  form  of  their  shell  or  by  the  arrangement  and  position  of  their 
flues  or  tubes.  The  class  of  "sectional"  or  "titbuloits  boilers"  will  be  considered 
separately  in  section  10,  chapter  xi. 

Boiler-shells  are  made  rectangular  or  cylindrical,  or  present  various  combinations  of 
rectangular  and  cylindrical  figures. 

The  rectangular  shell  possesses  the  great  advantage  that  it  is  easily  adapted  to  any 
arrangement  of  the  internal  parts  and  to  the  space  assigned  to  the  boiler  in  the  vessel. 


124  STEAM  BOILERS.  CHAP.  VII. 

The  furnaces,  connections,  tubes,  and  the  steam  and  water  spaces  may  be  arranged  in 
the  most  advantageous  manner,  as  well  with  respect  to  evaporative  efficiency  as  with 
respect  to  accessibility  and  economy  in  weight  and  space. 

The  cylindrical  shell  has  the  advantages  of  strength  and  of  simplicity  of  construction  ; 
but  the  circular  form  restricts  within  narrow  limits  the  choice  of  the  form,  arrangement, 
and  proportions  of  the  internal  parts  ;  the  steam-space  is  small  relatively  to  the  height 
of  the  boiler,  and  the  water-level  is  contracted ;  much  space  in  the  vessel  is  wasted  in 
the  spandrels  formed  by  the  shells  of  adjacent  boilers.  All  these  objectionable  features 
become  more  exaggerated  as  the  diameter  of  the  boiler  decreases  ;  besides,  with  a  dimin- 
ished diameter  the  number  of  the  boilers  has  to  be  increased,  and  consequently  the 
number  of  separate  attachments,  thus  increasing  the  cost,  the  weight,  and  the  liability 
of  the  boilers  to  derangement. 

The  form  given  to  the  shell  of  boilers  presents  often  a  combination  of  rectangular 
and  cylindrical  figures  ;  in  this  manner  a  compromise  is  effected  between  the  respective 
advantages  and  disadvantages  of  rectangular  and  cylindrical  boilers. 

Shells  having  an  approximately  oval  cross-section  have  been  extensively  used  of  late 
in  English  naval  vessels,  with  steam-pressures  of  60  or  70  Ibs.  above  the  atmosphere. 
The  furnaces  in  these  boilers  are  cylindrical,  and  when  the  larger  diameter  of  the  oval 
shell  is  placed  horizontally  furnaces  of  larger  diameter  can  be  used  than  with  circular 
boilers  of  equal  height.  When  the  larger  diameter  of  the  oval  shell  is  placed  vertically 
a  larger  and  higher  steam-space  is  obtained  for  the  same  amount  of  grate-surface. 
With  the  oval  shell  the  principal  advantage  of  the  circular  shell  is  sacrificed — viz.,  the 
absence  of  bracing  and  the  uniform  distribution  of  the  strain. 

Boiler-shells  have  been  formed  of  a  number  of  circular  arcs  joined  to  one  another 
and  tied  together  at  their  junction  by  braces,  forming  chords  of  these  arcs.  This  sys- 
tem, as  developed  by  Charles  E.  Emery,  is  illustrated  in  figure  92,  and  the  proper  mode 
of  bracing  such  structures  is  discussed  in  section  7,  chapter  vi.  This  system  enables  us 
to  extend  the  boiler  in  the  direction  of  its  length  and  height  indefinitely  as  in  the 
rectangular  boiler,  and  independently  of  the  radius  of  the  circular  arcs  ;  but  the  advan- 
tages of  the  simple  circular  shell— viz.,  absence  of  bracing,  simplicity  of  construction, 
and  accessibility — are  completely  sacrificed.  (See  section  1,  chapter  ix.) 

The  characteristic  features  of  flue  and  tubular  boilers  will  be  discussed  in  sections  1 
and  2,  chapter  xi.,  where  illustrations  of  several  kinds  of  marine  flue-boilers  will  be 
given. 

Tubular  boilers  have  superseded  entirely  flue-boilers  for  marine  purposes  ;  but  flues 
are  sometimes  used  in  them  in  combination  with  tubes. 


SBC.  3.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  125 

Tubular  boilers  may  be  divided  into  two  grand  groups — viz.,  1st,  the  water-tube  type, 
embracing  all  those  boilers  in  which  the  larger  portion  of  the  heating-surface  is  arranged 
in  tubes  containing  the  water  and  having  their  exterior  surfaces  acted  upon  by  the 
gaseous  products  of  combustion  ;  2d,  the  fire-tube  type,  embracing  all  those  boilers  in 
which  the  larger  portion  of  the  heating-surface  is  arranged  in  tubes  having  their  exterior 
surfaces  surrounded  by  the  water  and  their  interior  surfaces  acted  upon  by  the  gaseous 
products  of  combustion,  which  pass  through  them  on  their  way  from  the  furnace  to  the 
chimney.  Each  one  of  these  groups  may  be  subdivided  according  to  the  position  of 
the  tubes,  whether  vertical,  .inclined,  or  horizontal,  and  according  to  their  location — 
viz.,  whether  they  are  placed  above,  behind,  or  at  the  sides  of  the  furnaces.  The  con- 
siderations governing  the  choice  of  location  and  position  of  the  tubes  in  marine  boilers 
are  briefly  stated  in  section  3,  chapter  xi. 

"  In  the  present  state  of  marine  steam-engineering  the  choice  of  boilers  may  be  con- 
sidered as  restricted  to  the  vertical  water-tube  and  the  horizontal  fire-tube  boilers,  both 
having  their  tubes  arranged  above  their  furnaces."  ...  "  Recourse  will  be  had  to 
other  arrangements  of  tubes  relatively  to  the  furnaces  only  when  considerations  quite 
independent  of  boiler-construction  control ;  as,  for  example,  in  light-draught  vessels  of 
war,  where  it  is  a  sine  qua  non  that  the  entire  boiler  and  its  dependencies  be  placed 
below  the  water-level.  But  wherever  the  choice  is  not  thus  trammelled  one  of  the 
above  types  will  certainly  be  selected ;  because,  in  a  given  space,  both  on  the  vessel's 
floor  and  cubically,  they  allow  the  proper  distribution  and  proportion  of  parts,  and  the 
obtaining  of  the  maximum  economic  and  potential  evaporation  with  the  least  weight, 
cost,  and  external  surface  for  radiation ;  also,  with  the  least  weight  of  contained 
water,  and,  when  placed  in  pairs  facing  each  other — the  fire-room  being  in  common — 
with  the  least  space  for  fire-room.  These  types  are  the  most  convenient,  too,  for  repair, 
examination,  and  sweeping,  all  of  which  can  be  done,  without  trouble  or  special  provi- 
sion, from  the  fire-room,  whence  access  is  easily  had  to  the  interior."  (IsTierwood, 
'  Experimental  Researches,"1  vol.  ii.) 

Plates  VI.,  VII.,  and  XVII.  represent  the  two  kinds  of  boilers  which  were  in  gen- 
eral use  in  United  States  naval  vessels  while  the  working  pressure  of  steam  did  not 
exceed  45  Ibs.  per  square  inch  above  the  atmosphere — viz.,  the  vertical  water-tube 
boiler  of  the  Martin  type,  and  the  horizontal  fire-tube  boiler,  both  having  a  rectangular 
shell  and  the  tubes  placed  over  the  furnaces.  The  relative  evaporative  efficiency  of 
these  two  types  of  boiler,  as  determined  by  numerous  experiments  conducted  under  the 
direction  of  the  Bureau  of  Steam-Engineering  of  the  United  States  Navy  Department,  is 
as  follows :  When  each  boiler  has  25  square  feet  of  heating-surface  per  square  foot  of 


126  STEAM  BOILERS.  CHAP.  VII. 

grate-surface,  a  calorimeter  equal  to  one-eighth  of  the  grate-surface,  and  a  chimney  60 
feet  high,  the  boiler  being  placed  in  the  hold  of  the  vessel  and  the  air  having  to  reach 
the  ashpits  through  restricted  hatches  from  the  upper  deck,  the  maximum  rate  of  com- 
bustion with  natural  draught  is  for  the  horizontal  fire-tube  boiler  16  Ibs.  of  anthracite 
per  square  foot  of  grate,  and  for  the  vertical  water-tube  boiler  12£  Ibs.  of  anthracite  per 
square  foot  of  grate  ;  and  with  these  rates  of  combustion  the  former  will  furnish  4.36 
per  cent,  more  steam,  but  at  the  expense  of  28  per  cent,  more  fuel.  With  the  above 
proportions  the  space  occupied  by,  and  the  weight  of,  the  boiler  proper  and  the  watei 
contained  in  it  will  each  be  a  few  per  cent,  less  with  the  vertical  water-tube  than  with 
the  horizontal  fire-tube  boiler.  The  latter  has  the  practical  advantages  that  the  tubes 
are  more  easily  swept  and  that  leaky  tubes  are  easily  plugged,  even  while  the  boiler  is 
in  operation,  and  can  be  taken  out  and  replaced  without  disturbing  the  bracing  of  the 
boiler. 

The  boiler  of  the  U.  S.  S.  LacJcawanna  (Plates  VI.,  VII.),  containing  seven  furnaces 
with  an  aggregate  grate-surface  of  136.5  square  feet,  and  having  a  length  of  25  feet,  is 
as  large  as  it  is  convenient  to  build  rectangular  boilers,  on  account  of  the  limit  imposed 
by  the  size  of  the  boiler-hatches. 

Rectangular  boilers  have  been  built  in  some  instances  with  two  tiers  of  furnaces, 
placed  directly  over  one  another ;  each  pair  of  furnaces  discharging  their  gases  into  a 
common  back-connection  and  through  a  common  set  of  tubes.  This  arrangement  has 
been  adopted  to  augment  the  area  of  grate-surface  contained  within  a  single  shell  with- 
out increasing  the  length  and  breadth  of  the  boiler,  when  an  increase  of  height  was  ad- 
missible. This  arrangement  has,  however,  not  given  satisfactory  results ;  the  upper 
tier  of  furnaces  obstructs  the  free  escape  of  steam  generated  on  the  lower  furnace- 
crowns  ;  since  a  platform  has  to  be  built  to  fire  the  upper  furnaces,  fan-blowers  are 
required  to  furnish  a  sufficient  air-supply  to  the  lower  furnaces  and  to  ventilate  the 
lower  fire-room. 

With  cylindrical  shells  vertical  water-tubes  cannot  be  used  without  increasing  greatly 
the  amount  of  stayed  surfaces.  They  may,  however,  be  used  advantageously  in  oval 
shells  in  which  the  larger  diameter  forms  the  vertical  axis,  as  the  flat  portions  of  the 
shell  may  be  tied  directly  to  the  flat  vertical  sides  of  the  tube-boxes. 

Fire-tubes,  placed  in  the  direction  of  the  axis  of  the  cylinder,  can  be  arranged  in  the 
most  convenient  manner,  and  are  used  almost  exclusively,  in  cylindrical  marine  boilers. 

In  cylindrical  boilers  the  diameter  of  the  shell  limits  the  number  and  the  diameter 
of  the  furnaces.  In  the  type  of  boilers  represented  on  Plates  VIII.,  XI.,  and  XII., 
having  a  cylindrical  shell  and  cylindrical  furnaces,  and  horizontal  fire-tubes  arranged 


SEC.  3.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  127 

above  the  furnaces,  when  the  shell  is  from  seven  to  eleven  feet  in  diameter  the  number 
of  furnaces  is  generally  two,  and  when  the  shell  is  from  eleven  to  fourteen  feet  in  dia- 
meter the  number  of  furnaces  is  generally  three.  When  the  working  pressure  of  steam 
is  as  high  as  80  Ibs.  above  the  atmospheric  pressure  the  diameter  of  boilers  seldom  ex- 
ceeds fourteen  feet,  on  account  of  the  difficulty  of  working  the  heavy  plates  required  in 
the  construction  of  the  shell.  When  the  shell  is  less  than  seven  feet  in  diameter  two 
cylindrical  furnaces  may  be  used  with  the  tubes  arranged  behind  the  furnaces  ;  but  with 
return-tubes  a  single  cylindrical  furnace  has  to  be  used,  and  the  tubes  have  to  be  ar- 
ranged partly  at  the  sides  of  the  furnace.  With  the  latter  arrangement  it  is  found  that 
the  draught  is  relatively  sluggish  (see  "Boiler  Experiments,"  Franklin  Institute  Jour- 
nal, March,  1879),  and  the  furnace-crowns  are  inaccessible  for  cleaning  unless  the  tubes 
are  removed  ;  in  case  the  furnace  is  of  large  dimensions  and  the  tubes  are  closely  spaced 
the  circulation  of  the  water  is  imperfect  and  the  steam  escapes  with  difficulty  from  the 
furnace-crowns.  This  arrangement  should  be  avoided  in  marine  boilers  where  salt 
water  has  to  be  used ;  but  it  is  often  used  to  advantage  in  boilers  of  steam-launches  and 
similar  small  craft,  supplied  with  fresh  water  from  tanks  and  using  a  steam-blast, 
because  with  this  arrangement  the  bulk  of  the  boiler  and  the  weight  of  water  contained 
in  it  may  be  reduced  considerably.  (See  Plate  XVI.) 

The  boiler  represented  on  Plate  XV.,  having  furnaces  at  both  ends,  illustrates  a 
method  of  increasing  the  grate-surface  within  a  shell  of  a  given  diameter  without  af- 
fecting the  proportions  of  heating-surface,  calorimeter,  and  steam-room  to  grate-sur- 
face. Compared  with  two  single-end  boilers  of  equal  diameter,  grate-surface,  and  pro- 
portion of  internal  parts,  the  bulk,  weight,  and  cost  of  construction  of  the  double-end 
boiler  is  less,  owing  to  the  omission  of  the  two  back-heads  and  the  attachment  of  braces 
to  them  ;  with  the  number  of  boilers  the  number  of  valves,  pipes,  and  other  apparatus 
required  for  each  separate  boiler  is  likewise  diminished;  the  total  space  in  the  vessel 
occupied  by  double-end  boilers  is  somewhat  greater,  because  each  end  requires  a  sepa- 
rate fire-room. 

In  order  to  reduce  still  more  the  length  and  the  weight  of  double-end  boilers  the 
water-space  separating  the  back-connections  of  each  pair  of  opposite  furnaces  is  some- 
times omitted,  so  that  the  two  furnaces  discharge  their  gases  into  a  common  back-con- 
nection. But  with  this  arrangement  the  action  of  the  two  currents  of  gas  entering  the 
back-connection  from  opposite  sides  is  prejudicial  to -an  active  and  reliable  draught. 

The  boiler  of  the  U.  S.  S.  Daylight  (figure  1,  Plate  III.)  illustrates  a  type  of  boiler 
frequently  used  on  American  steam-vessels.  The  front  portion  of  the  shell  is  made 
rectangular  in  plan,  with  flat  sides  and  a  semi-cylindrical  top  ;  the  back  portion  is  cylin- 


Of    THE 

UNIVERSITY 

OF 


128  STEAM  BOILERS.  CHAP.  VII. 

drical,  with  its  top  a  horizontal  continuation  of  the  top  of  the  semi-cylindrical  front  por- 
tion. The  cylindrical  portions,  which  are  of  an  oval  cross-section  in  the  present  exam- 
ple, are  more  frequently  of  a  circular  cross-section.  The  rectangular  front  admits  of 
the  most  advantageous  proportions  of  the  furnaces,  and  the  use  of  the  cylindrical  form 
for  the  rest  of  the  shell  simplifies  the  construction.  A  high  steam-drum  surrounding 
the  uptake  affords  additional  steam-room  and  superheating  surface.  Flues  of  large 
diameter  extend  from  the  combustion-chambers  at  the  back  of  the  furnaces  to  the  back- 
connections,  and  the  horizontal  return-tubes  are  likewise  relatively  of  a  large  diameter 
and  of  great  length.  This  arrangement  is  favorable  to  a  high  rate  of  combustion  ;  the 
draught  is  frequently  forced  by  fan-blowers  in  this  type  of  boiler. 

Figures  2  and  3,  Plate  III.,  illustrate  arrangements  of  the  tubes  adopted  in  marine 
boilers  where  the  height  of  the  boilers  has  to  be  reduced  at  the  expense  of  the  room 
occupied  on  the  floor  of  the  vessel.  The  lower  flue  in  the  boilers  of  the  U.  S.  S.  Ma- 
TiasTta  is  sometimes  omitted,  the  vertical  water-tubes  being  arranged  directly  behind 
the  furnaces  ;  in  other  boilers  the  vertical  water-tubes  have  been  arranged  at  the  sides 
of  the  furnaces,  the  upper  tube-sheet  being  on  a  level  with  the  furnace-crown.  A  simi- 
lar arrangement  is  sometimes  adopted  with  horizontal  fire-tubes.  All  these  arrange- 
ments present  the  advantages  that  the  water-surface  from  which  the  steam  escapes  is 
about  twice  as  great  as  when  the  tubes  are  placed  above  the  furnaces,  and  that  the 
steam  generated  on  the  furnace-crowns  escapes  freely,  not  having  to  pass  through  the 
narrow  water-spaces  in  or  between  the  tubes.  These  advantages  are  of  great  importance 
when  a  high  rate  of  combustion  is  employed. 

The  type  of  boiler  having  horizontal  fire-tubes  placed  directly  behind  the  furnaces 
is  called  the  "locomotive  type"  because  this  arrangement  is  always  adopted  in  the 
boilers  of  locomotives.  Figure  2,  Plate  III.,  illustrates  this  arrangement  adapted  to  a 
marine  boiler  with  a  rectangular  shell,  while  Plates  IV.  and  V.  illustrate  the  same  type 
of  boiler  built  for  railroad  purposes.  In  the  latter  the  front  portion  of  the  shell  is 
always  rectangular  in  plan,  with  flat  sides,  in  order  to  get  a  roomy  furnace,  and  the  top 
is  generally  made  semi-cylindrical ;  the  back  portion  of  the  shell  is  cylindrical.  The 
tubes  are  of  small  diameter  and  great  length,  and  are  closely  spaced  in  order  to  get  a 
large  heating-surface  within  a  small  space.  All  the  water-spaces  are  narrow  ;  the  whole 
boiler  is  made  long  but  low  ;  its  bulk  and  weight  are  reduced  as  much  as  possible.  It 
is  designed  to  generate  steam  rapidly,  and  to  have  a  high  economic  and  potential  evapo- 
ration ;  it  is  always  worked  with  a  steam-blast. 

The  same  type  of  boiler  is  frequently  used  for  marine  purposes,  in  steam-launches 
and  similar  small  craft,  when  fresh  water  is  used  to  feed  the  boiler.  In  case  salt  water 


SEC.  3.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  129 

has  to  be  used  at  times  it  is  better  to  make  the  whole  shell  cylindrical,  in  order  to  re- 
duce the  stays  and  braces  required  to  a  minimum. 

The  vertical  fire-tube  boiler  having  a  cylindrical  shell  (see  figure  1,  Plate  XXVIII.) 
is  capable  of  a  high  rate  of  combustion,  but  its  economic  evaporative  efficiency  is 
small,  unless  the  tubes  are  made  very  long  and  the  proportion  of  heating  to  grate  sur- 
face is  unusually  large.  The  water-level  is  carried  some  distance  below  the  upper  tube- 
sheet,  and  the  upper  ends  of  the  tubes  and  the  uptake  furnish  superheating-surface. 
The  bulk  and  weight  of  this  boiler  are  relatively  small.  This  type  is  frequently  used 
for  boilers  of  steam-launches  and  road-engines.  It  has  also  been  used  for  large  marine 
boilers,  but  is  not  well  suited  for  them,  because  the  arrangement  of  the  tubes  makes  the 
interior  of  the  boilers  almost  inaccessible,  and  the  great"  length  of  the  tubes  makes  it 
difficult  to  clean  them  or  remove  and  replace  them. 

Dicker  son's  marine  boiler  had  a  rectangular  shell ;  inclined  water- tubes  were  placed 
directly  over  the  furnace,  and  the  products  of  combustion  rising  from  the  grate  envel- 
oped these  tubes  and  then  passed  through  vertical  fire-tubes,  placed  above  them  in  the 
steam-space,  into  the  uptake.  The  front  and  back  of  the  boiler  had  large  open- 
ings, closed  by  cast-iron  covers  secured  by  bolts,  to  make  the  water-tubes  accessible. 
This  boiler  may  be  regarded  as  a  connecting-link  between  the  preceding  types  of 
tubular  marine  boilers  and  the  sectional  water -tube  boilers  described  in  section  10, 
chapter  xi.  With  the  rate  of  combustion  usual  in  marine  boilers  the  steam  generated 
in  the  inclined  water-tubes  escaped  with  difficulty,  and  the  gaseous  products  of  com- 
bustion entered  the  uptake  at  a  high  temperature ;  in  consequence  the  tubes  were  soon 
burnt,  and  the  boilers  have  gone  out  of  use  after  a  short  trial 


130 


STEAM  BOILERS. 


CHAP.  VII. 


TABLE    XXIL, 
SHOWING  THE  DIMENSIONS,  PROPORTIONS,  AND  WEIGHTS  OF  BOILERS  OF  VARIOUS  TYPES. 


z 

3 

3 

4 

5 

6 

7 

8 

Name  of  vessel. 

Number  of  plate. 

Description  of  boiler. 

Number  of  boilers. 

Total  number  of  furnaces. 

Total  area  of  grate-surface  in 
square  feet. 

Square  feet  of  water-heating 
surface  per  square  foot  of 
grate-surface. 

Square  feet  of  steam-super- 
heating surface  per  square 
foot  of  grate-surface. 

Square  ft.  of  grate-surface  per 
sq.  ft.  of  cross-area  through 
tubes  or  flues  for  draught. 

Square  feet  of  grate-surface 
per  square  foot  of  cross-area 
of  smoke-pipe. 

U.  S.  S.  Lackawanna  

(  VI.  ) 

^and  \ 

Rectangular  shell  ;  vertical  water-tubes  ; 

VII. 
Ill 

5-    I' 

o 

7  018 

"       Plymouth         .     . 

XVII 

5.870 

"       Daylight 

III 

Kansas  

in. 

XXI. 

Rectangular  shell  ;  locomotive  type  

2 

6 

108.00 
64  58 

28.500 

0.741 

5-455 
8.772 

12.401 

XXI. 

"       Nipsic  

XII. 

6 

il       Miantonomoh  and  class.  . 

VIII. 

Cylindrical  shell  ;  horizontal  return  fire- 
tubes  

6 

18 

XI. 

ooo 

600 

u      Lord  of  the  Isles  

XV. 

3* 

"      Estelle 

XXVII 

18  i8 

—^j 

-_^-, 

7  SAT 

*  Two  telescopic  smoke-pipes. 


t  Water-level  9  inches  above  tubes. 


Szc.  3. 


DESIGN,  DRAWINGS,  AND  SPECIFICATIONS. 


131 


TABLE  XXII.—  (Continued.) 
SHOWING  THE  DIMENSIONS,  PROPORTIONS,  AND  WEIGHTS  OF  BOILERS  OF  VARIOUS  TYPES. 


9 

10 

II 

12 

13 

M 

15 

16 

17 

18 

19 

20 

21 

23 

23 

S 

.5 

M4 

So 

1 

t*  r  w 

c 

.£ 

.s 

c 

*o 

•s 

C-s 

•o 

6-S 

Height  of  smoke-pipe  abo 
'level  of  grate,  in  feet. 

Capacity  of  steam-room 
boiler-shell,  in  cubic  feet 

Capacity  of  steam-room 
steam-drums,  in  cubic  fci 

II 
II 

S« 

*i 

MJ 

a  si 

lrf 

Total  capacity  of  steam-roo 
in  cubic  feet. 
1 

Weight  of  boilers,  includl 
doors,  uptakes,  plates,  et 
but  excluding  smoke-pi 
and  grate-bars. 

1 

! 

(ft 

*o  . 

at 

_-a 

If 
fl 

"i 
1 

"3 
.4 

.-I! 

«a 

1 

1 

o 

2 

fj 

*\ 

si 
1* 

Weight  of  water  in  boilers 
pounds. 

o. 
2 

o 

V 

Sj 

"o.e 
ll 

0    * 

1 

2» 
S=* 

S 

^"V 

—  e 

}] 

u  " 

Length  occupied  by  boiU 
and  fire-room  in  the  vess 

Width  occupied  by  boilers  a 
fire-room  in  the  vessel. 

Working  pressure  of  stea 
in  pounds  per  square  in 
above  the  atmosphere. 

59.50 

866 

.... 

866 

93,000 

5,30° 

8,590 

106,890 

68,500 

8.00 

29.00 

20.166 

40 

56.00 

I  loot 

.... 

K4 

»324 

265,000 

«.3fa* 

20,000 

306,362 

H5,ooot 

9.00 

.... 

38-50 

27.500 

40 

43.50 

670 

130 

800 

10.66 

18.00 

25 

653 

873 

760 

53.50 

740* 

140 

20 

900 

185.000 

14,150 

IO,OOO 

209,350 

78,360$ 

9.00 

9.00 

3I-50 

28.25 

so 

.... 

'5*) 

300 

135 

2024 

374.000 

7,800 

24,000 

405,800 

igi^ooot 

12.13 

12.75 

38.00 

34-00 

so 

35 

60 

8  740 

15.6 

8.00 

So 

680 

27.75 

28.500 

28.00 

i7-24i 

9-4 

36.64 





16,500 

1.  100 

11.25 

18.00 

8.250 

200 

Water-level  6  inches  above  tubes. 


{  Half  capacity  of  coil. 


132 


STEAM  BOILERS. 


CHAP.  VII. 


TABLE    XXIII. 

SHOWING  THE  ECONOMIC  EVAPORATION  OF  BOILERS  OF  VARIOUS  TYPES,  WITH  DIFFERENT  RATES 
OF  COMBUSTION,  AND  WITH  DIFFERENT  PROPORTIONS  OF  CALORIMETER,  HEATING-SURFACE, 
AND  GRATE-SURFACE. 


I 

a 

3 

4 

S 

6 

7 

8 

9 

IO 

V 

i"o 

sil 

E  "  v 

ES" 

•a  ii^jj 

"3.5 

•5 

I. 

</]  o 

•If 

rt  A 

rt  J3  fO 
3  C  ** 

III 

•C  E'o 

v! 

Ha 

lai-j 

1| 
£•3 

ll 
|| 

C 

u  rt 

V  3 

||j 

2  |- 

|12 

4)-C         o 

t.    a.0^    y 

2  = 

& 

1 

Name  of  vessel. 

*     «  t!i 

Jl 

Type  of  boiler. 

-sj 

*-»  «ii  *•  bo 

•S  o 

C  0  o- 
rt       o 

fill 

||| 

*o  — 

II 

1 

O.«l 

i? 

*2i  o  w 

t)  "    4> 

|!|| 

fll 

llil 

1"=  =-2 

111 

u  °  > 

2j 

E  o 

IM 

O 

ii 

3.0 

g  3  S  0 

V   U 

a 

» 

V) 

t2 

0. 

£ 

(2 

H 

Q 

*  U.  S.  S.  Mahaska. 

III. 

Verti'l  water-tubes 

29.275 

7.018 

5-505 

0.228 

13.873 

93.04 

298.2 

I863 

(Bartol's  patent). 

*       "       Daylight... 

III. 

Horizontal    return 

30.355 

7.870 

6.5II 

0.214 

11.199 

75-10 

280.1 

I863 

fire-tubes. 

*       "               "     ... 

11 

41 

30.355 

7.870 

8.270 

0.272 

11.879 

79-66 

261.0 

1864 

*       "       Kansas... 

III. 

Locomotive  type.  . 

28.500 

5-455 

14.103 

0.596 

10.196 

68.38 

495-7 

1863 

*       ii             ii 

" 

" 

28.500 

6.601 

13.124 

0.552 

10.790 

72.36 

466.9 

1863 

*       ii             ii 

" 

" 

28.500 

8.148 

13.176 

0.565 

10.789 

72-35 

535-6 

1863 

*       ii             ii 

" 

" 

28.500 

10.313 

10.754 

0.464 

11.570 

77-59 

497-5 

1863 

*       "       Shockokon 

XXI. 

21.058 

8.772 

15  209 

O.721 

8673 

58.16 

1864 

*       ii             ii 

21.058 

"•//** 

8.772 

8.843 

"•  i  "  j 
.0.420 

8.660 

jw.  j 

58.08 

.... 

*  ****^ 

1864 

*       "       Morse  

XXI. 

Double-return 

21.901 

9-357 

9-372 

0.428 

10.257 

68.78 

1863 

drop-flues. 

f  S.  S.  Estelk  .... 

XXVII. 

Herreshoff      coil- 

13.283 

1.511$ 

10.698 

0.805 

9-938 

66.64 

.... 

1877 

boiler. 

*  Isherwood,  'Experimental  Researches/  vol.  ii.  t  *  Report  of  Board  of  United  States  Naval  Engineers,' 1878. 

$  Proportion  of  grate-surface  to  cross-area  of  chimney  =  7.811  to  i. 


Sue.  4.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  133 

4.  Space  and  Weight  required  for  Boilers  of  a  given  Power  (Isfterwood, 
'Experimental  Researches •,'  vol.  ii.) 

"  In  a  steamer  a  certain  space  is  to  be  allotted  to  the  boiler,  fire-room,  and  coal  for  a 
given  speed  to  be  maintained  a  given  time ;  and  the  problem  is  so  to  apportion  them 
that  this  space  shall  be  a  minimum.  To  fulfil  the  speed  condition  a  certain  weight  of 
steam  per  hour  must  be  furnished.  Now,  if  a  boiler  with  a  high  rate  of  combustion  be 
employed  a  less  space  will  be  required  for  it  and  its  fire-room,  but  more  space  will  be 
required  for  the  coal,  as  the  economic  evaporation  will  be  less ;  and,  vice  versa,  if  a 
boiler  with  a  low  rate  of  combustion  be  employed  a  greater  space  will  be  required  for 
it  and  its  fire-room,  but  less  space  will  be  required  for  the  coal,  on  account  of  its  greater 
economic  evaporation.  It  is  evident  there  is  a  point  where  the  aggregate  space  is  a 
minimum.  If  the  cost  of  fuel  be  considered  an  item  of  importance,  it  extends  the  prob- 
lem, in  a  commercial  vessel,  to  whether  it  is  not  advantageous  to  employ  a  boiler  of  still 
lower  rate  of  combustion  and  higher  economic  efficiency,  and  take  the  additional  space 
required  for  it  from  the  portion  allowed  to  cargo.  In  a  war-steamer  this  additional 
space  would  be  at  the  expense  of  its  military  power. 

"  In  the  following  table  will  be  found  the  solution  of  the  above  problem  for  the  hori- 
zontal fire-tube  boiler  having  the  tubes  above  the  furnaces.  The  determination  is  made 
for  the  case  in  which  the  vessel  is  to  carry  a  supply  of  fuel  sufficient  for  200  hours' 
maximum  steaming.  .  .  .  Further,  the  determination  is  made  both  for  aggregate 
space  occupied  and  weight  carried,  for  the  fuel,  and  the  boilers  and  fire-room. 

"In  making  these  calculations  the  boiler  is  assumed  to  be  10  feet  3  inches  long  at 
the  level  of  the  grates,  9  feet  9  inches  high,  and  of  sufficient  width  or  frontage  to  give 
the  requisite  grate-surface  with  furnaces  3  feet  wide,  containing  grates  6  feet  6  inches 
long.  The  fire-room  is  assumed  to  extend  in  the  fore  and  aft  direction  of  the  vessel, 
and  to  be  8  feet  6  inches  wide,  the  boilers  being  arranged  on  each  side  of  it  in  oppo- 
site pairs. 

"The  ratio  of  the  heating  to  the  grate  surface  is  taken  at  25  to  1,  and  the  calori- 
meter at  one-eighth  of  the  grate-surface. 

"The  thickness  of  the  plate  for  the  bottom  of  the  boiler,  and  for  the  furnaces  and 
the  ashpits,  is  taken  at  f  of  an  inch,  for  the  tube-plates  at  £  inch,  and  for  all  other 
parts  at  ^  of  an  inch ;  all  seams  are  taken  to  be  double-riveted,  and  the  boiler  to 
be  braced  for  a  working  pressure  of  40  pounds  per  square  inch  above  the  atmos- 
phere. .  .  . 

"  The  weights  taken  for  the  boiler  are  the  actual  weights  as  determined  by  weighing 
exactly  such  boilers  after  completion.  These  weights  include  not  only  the  boiler  pro- 


134  STEAM  BOILERS.  CHAP.  VH. 

per,  but  everything  appertaining  to  it,  as  grate-bars,  smoke-pipe,  doors,  plates,  valves, 
pipes,  felt  and  sheet-lead  covering,  floor-plates  of  fire-room,  and  water  in  boilers.  .  .  . 

"The  fuel  is  to  be  anthracite,  with  one-sixth  of  refuse,  and  the  space  occupied  by 
every  53£  pounds  of  it  to  be  1  cubic  foot,  which  is  the  average  of  bunker-stowage  with 
this  coal.  .  .  .  The  maximum  weight  of  steam  to  be  furnished  per  hour  is  taken  at 
60,000  pounds.  .  .  . 

"  We  find,  on  examining  the  column  of  space  occupied  by  the  aggregate  boiler,  fire- 
room,  and  anthracite,  .  .  .  that,  leaving  wholly  out  of  view  the  economic  evaporation 
by  the  anthracite,  the  best  rate  of  combustion  for  obtaining  in  a  given  space  the  great- 
est quantity  of  steam  per  hour  during  200  hours  is  13  pounds  of  anthracite  per  square 
foot  of  grate-surface  per  hour.  ...  If  some  importance  be  given  to  the  economy  of  the 

fuel  we  perceive  that,  by  reducing  the  rate  of  combustion  to  10  pounds  of  anthracite, 

(Q  oca  _  g  23g  \ 

g  OQQ  —  X  100  )  =  9.14  per  centum 


.  /59001  -  55826  \ 

by  increasing  the  space  occupied  (  --  55326      ~  x       /  =         Per  centum  »  •   •   •  tne 

minimum  aggregate  weights  of  boiler  and  its  appurtenances,  and  of  the  anthracite,  cor- 
respond to  a  rate  of  combustion  of  11  pounds  of  anthracite  per  square  foot  of  grate- 
surface  per  hour."  It  is  evident  that  when  the  maximum  supply  of  steam  is  to  be 
furnished  for  a  greater  or  less  length  of  time,  the  weight  and  space  occupied  by  the 
boiler  and  fire-room  remains  the  same  for  the  respective  rates  of  combustion,  while  that 
of  the  anthracite  increases  or  decreases,  as  the  case  may  be. 


SEC.  4. 


DESIGN,  DRAWINGS,  AND  SPECIFICATIONS. 


135 


TABLE  XXIV. 

EXHIBITING  THE  SPACE  AND  WEIGHT  REQUIRED  WITH  THE  HORIZONTAL  FIRE-TUBE  BOILER 
HAVING  A  RECTANGULAR  SHELL  AND  THE  TUBES  ARRANGED  ABOVE  THE  FURNACES,  AND 
WITH  ANTHRACITE  WITH  ONE-SIXTH  REFUSE,  TO  FURNISH  A  GIVEN  SUPPLY  OF  STEAM  PER  HOUR 
FOR  200  HOURS  WITH  DIFFERENT  RATES  OF  COMBUSTION. 


"So           |jSJj                   i 

s-         £-.«              3 

Space. 

Weight. 

3O                  3   •»* 

£ 

S.2 

O 

~S_°0    . 

iASfe 

g-si." 

I    «j  "T-i   r-   *• 

3  *•  i~   r   *• 

"•3«'  -IE" 

"  > 

S"g  • 

,s 

ft 

Mil 

>  5J£J= 

1 

slfl 

•1*5 

2  =   3  3 

y  rt  i;-—  rt 

1  *-^±J7.-= 

•lis-s 

a-S  a  s 

?!! 

il< 

-   3^ 

iN« 

S2-=^ 
*  3  K-o 
t~"c  rt  = 

e  ii 

|| 

*2 

ffi 

iail 

SiJll 

""-  c  e      '»"!!•               •-  Z  O.3 

ssis^5-s      -si  -a 
lltflj'll     fls'5- 

ill 

•M 

111 

*s*i    u 

till       ii 

lilli 

lilli 

illlll 

3  ccn  a^5-o 

l^illi] 

w  ^  o  « 

|ij 

- 

0, 

z 

u 

u 

U 

n 

* 

^ 

6 

9.383 

7 
1,065.72 

54,240 

23,979 

78,219 

1,231,866 

1,278,880 

2,510,746 

7 

9.338 

917.91 

46,717 

24,095 

70,8l2 

1,061,012 

1,285,067 

2,346,079 

8          9.258 

8io.ii 

41,230 

24,303 

65,533 

936,406 

1,296,160 

2,232,566 

9          9-I50 

728.60 

37,082 

24.590 

61,672          i          842,189 

1,311,467 

2,153,656 

10 

8.989 

667.48 

33.971 

25,030 

59,001 

771,540 

1,334.933 

2,106,473 

ii 

8.775 

620.32 

31,627 

25,641 

57,268 

717,028 

1,367,520 

2,084,548 

12 

8.524 

586.58 

29.907 

26,396 

56,303 

678,028 

1,407,787 

2,085,815 

13 

8.238 

560.25 

28,514 

27,312 

55,826 

647,593 

1,456,640 

2,104,233 

14 

7-934 

540.17 

27,492 

28,359 

55,851 

624,382 

1,512,480 

2,136,862 

15 

7.621 

524-87 

26,713 

29,524 

56,237 

606,697 

1,574,613 

2,181,310 

16 

7-343 

510.69 

25,991 

30,641 

56,632 

590,306 

1,634,187 

2,224,493 

17 

7.111 

496.33 

25,261 

31,641 

56,902 

573,708 

1,687,520 

2,261,228 

18 

6.887 

484.00 

24,633 

32,670 

57,303 

559,456   1,742,400 

2,301,856 

19 

6.690 

472-03 

24,024 

33.632 

57,656 

545,619   1,793,707 

2,339,326 

20 

6-547 

458.23 

23,322 

34,367 

57,689 

529,668 

1,832,907 

2,362,575 

21 

6404 

446.15 

22,707 

35.134 

57,841 

515,705 

1,873,813 

2,389.518 

22 

6.297 

433.17               22,046 

35.731 

57,777 

500,701 

1,905,653 

2,406,354 

23 

6.190 

42144                21,449 

36,349 

57,798 

487,142    1,938,613 

2,425,755 

24 

6.100 

409.84                20,859 

36,885 

57,744 

473,734 

1,967,200 

2,440,934 

136  STEAM  BOILERS.  CHAP.  VII. 

5.  Proportioning  the  Parts  of  a  Boiler. — In  the  following  special  regard  has 
been  had  to  the  ordinary  type  of  marine  boilers,  with  horizontal  fire-tubes  or  vertical 
water-tubes  arranged  over  the  furnaces,  and  burning  anthracite  coal  with  natural  chim- 
ney-draught, unless  the  conditions  are  otherwise  specified. 

The  length  and  the  width  of  the  grate  are  limited  to  such  dimensions  as  will  permit 
the  proper  management  of  the  fire,  especially  the  cleaning  of  the  back  and  of  the 
front  corners  ;  on  this  account  the  length  should  never  exceed  7  feet  nor  the  width  42 
inches ;  the  grate-surface  in  each  furnace  ranges  generally  between  18  and  21  square 
feet.  The  grate  slopes  downward  from  the  front  to  the  back,  at  the  rate  of  one  inch  or 
1J  inch  to  the  foot  in  the  length  of  the  grate  ;  this  arrangement  facilitates  the  firing  at 
the  back,  and  makes  the  furnace  roomier  at  the  same  time. 

The  ashpit,  even  when  partly  obstructed  by  ashes,  must  admit  a  sufficient  quantity 
of  air,  moving  at  a  low  velocity,  to  every  part  of  the  grate.  This  condition  will  gene- 
rally be  fulfilled  when  the  ashpit  is  made  roomy  enough  to  permit  the  working  of  the 
fire  from  below  the  grate.  With  dimensions  of  the  grate  as  given  above,  the  height  of 
the  ashpit-opening  in  front  varies  from  15"  to  18",  while  its  width  is  made  equal  to  that 
of  the  furnace. 

The  furnace  must  have  sufficient  height  above  the  grate  to  afford  room  for  the  gases 
to  mingle  thoroughly  and  to  permit  a  proper  working  of  the  fire.  The  height  of  the 
furnace-crown  above  the  grate  in  marine  boilers  burning  anthracite  coal,  with  natural 
draught,  averages  from  18  to  24  inches.  High  rates  of  combustion  necessitate  an  in- 
crease in  the  height  of  the  furnace  ;  in  locomotive  boilers  the  furnace  is  often  made  48 
inches  high.  Bituminous  coals  require  a  larger  combustion-chamber  than  anthracite. 

The  calorimeter  oner  the  bridge-wall  at  the  back  end  of  the  grate  should  be 
made  as  small  as  is  consistent  with  the  desired  rate  of  combustion,  in  order  to  in- 
crease the  velocity  of  the  gases  to  a  maximum  at  this  point,  and  cause  them  to  mingle 
thoroughly  as  they  emerge  into  the  combustion-chamber  or  back-connection.  The  area 
of  this  passage  is  made  from  |  to  ^  of  the  area  of  the  grate  in  marine  boilers  using  natu- 
ral draught ;  when  forced  draught  is  used,  and  the  rate  of  combustion  is  increased,  the 
area  of  this  passage  is  likewise  to  be  increased.  The  opening  should  extend,  if  possible, 
the  whole  width  of  the  grate,  the  area  being  regulated  by  the  height. 

The  ~back  smoTce-connection  should  be  as  spacious  as  possible  to  afford  the  gases 
room  and  time  to  complete  their  combustion  before  entering  the  tubes.  This  condition 
will  generally  be  fulfilled  when  sufficient  room  is  provided  to  admit  a  man  for  making 
examinations  and  repairs,  expanding  the  tube-ends,  calking,  etc.  ;  the  width  of  this 
chamber  ranges  generally  between  18  and  30  inches. 


SEC.  5.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  137 

The  calorimeter  through  or  between  the  tubes  varies  from  \  to  \  of  the  area  of  the 
grate-surface,  the  larger  area  being  used  for  the  higher  rates  of  combustion  ;  the  dia- 
meter of  the  tubes  depends  to  a  great  extent  on  the  amount  of  heating-surface  that  is 
to  be  placed  into  the  allotted  space.  The  diameter  of  horizontal  fire-tubes  varies  from 
2£  to  4£  inches  ;  smaller  tubes  are  liable  to  become  choked  with  soot  and  ashes,  unless 
a  very  strong  draught  is  produced  by  a  blast.  Vertical  water-tubes  are  commonly  made 
2  inches  in  diameter,  and  are  spaced  so  as  to  allow  from  1£  inches  to  If  inches  of  clear 
space  for  the  passage  of  the  gases. 

The  calorimeter  of  the  smoke-pipe  varies  from  \  to  £  of  the  area  of  the  grate.  When 
several  furnaces  empty  their  gases  into  a  common  chimney,  care  must  be  taken  that  the 
calorimeter  of  the  uptake  at  different  points  is  proportional  to  the  volumes  of  gas  that 
have  to  pass  such  points. 

The  total  heating-surface  of  marine  boilers  using  natural  draught  is  made  from  25 
to  35  times  the  area  of  the  grate-surface  for  rates  of  combustion  ranging  between  12  Ibs. 
and  22  Ibs.  of  coal  per  square  foot  of  grate  per  hour.  When  forced  draught  is  em- 
ployed the  heating-surface  must  be  increased  in  proportion  to  the  increased  rate  of  com- 
bustion ;  in  locomotives,  burning  as  much  as  120  Ibs.  of  coke  per  square  foot  of  grate 
per  hour,  the  heating-surface  is  about  90  times  the  area  of  the  grate-surface.  The  eva- 
porative efficiency  of  the  different  heating-surfaces  in  a  boiler  varies  greatly,  as  has 
been  shown  in  chapter  iii.  The  heating-surfaces  must  be  arranged  in  such  a  manner  as 
to  allow  the  steam  to  escape  from  them  as  soon  as  formed  ;  horizontal  water-tubes  are 
therefore  to  be  avoided,  as  well  as  extensive  flat  surfaces  for  the  bottom  of  flues  and 
smoke-connections.  By  rounding  the  corners  of  internal  square  passages  with  a  large 
radius  the  free  escape  of  the  steam  and  the  circulation  of  the  water  will  be  greatly  faci- 
litated, while  the  strength  of  those  parts  is  increased  at  the  same  time.  A  relatively 
small  portion  of  the  heating-surface  in  the  uptake  of  every  boiler  passes  through  the 
steam-space  ;  it  is  often  found  advantageous  to  increase  this  superheating-surface  by 
means  of  various  contrivances  that  will  be  described  in  a  subsequent  chapter.  (See 
section  3,  chapter  xiii.) 

The  water-spaces  surrounding  the  furnace  and  the  smoke-connections  should  never 
be  less  than  4  inches  in  the  clear,  and,  if  possible,  should  be  made  5£  inches  wide  in 
marine  boilers.  Sufficient  room  must  be  left  between  the  furnace  and  the  tubes  to  ad- 
mit a  man  to  the  interior  of  the  boiler  to  scale  the  crown-sheet  of  the  furnace  and  to 
make  repairs.  Manholes  provided  for  this  purpose  in  the  front  of  the  boiler  are  oval 
in  shape,  of  15*  X  12*  diameter ;  the  smallest  admissible  size  is  13*  x  11*. 

The  clear  space  left  for  this  purpose  above  the  furnace  is  also  necessary  on  account 


138  STEAM  BOILERS.  CHAP.  VII. 

of  the  rapid  formation  of  steam  on  the  furnace-crown,  as  it  facilitates  the  free  circulation 
of  the  water  ;  for  the  same  reason  it  is  not  advisable  to  make  the  furnaces  of  marine  boil- 
ers very  wide,  especially  when  the  tubes  are  placed  rather  close  to  the  furnace-crown. 

Horizontal  fire- tubes  returning  over  the  furnace  should  be  spaced  with  at  least  1  inch 
of  clear  space  between  them  in  a  horizontal  direction,  and  must  be  placed  in  vertical 
rows,  in  order  to  offer  the  least  obstruction  to  the  rising  steam-bubbles.  It  is  advisable 
to  leave  larger  spaces,  from  5  to  7  inches  wide,  between  the  tube-rows  at  intervals,  for 
the  passage  of  the  descending  currents  of  water. 

The  water  must  be  carried  at  such  a  height  above  the  back-connection  and  the  tubes 
that  they  are  not  bared  too  readily  through  irregularities  in  the  admission  of  the  feed- 
water,  excessive  foaming,  or  the  rolling  of  the  vessel.  With  horizontal  fire-tubes  the 
water-level  should  be  carried  not  less  than  6  inches  above  the  back-connection.  The 
area  of  the  water-level  should  always  be  as  large  as  possible,  to  prevent  foaming  and 
the  lifting  of  water. 

The  capacity  of  the  steam-space  depends  on  the  number  of  cubic  feet  of  steam  re- 
quired by  the  engine  in  a  unit  of  time.  It  should  be  of  sufficient  height  to  prevent  the 
lifting  of  the  water  into  the  steam-pipe.  (See  section  1,  chapter  xiii.) 

6.  Relative  Value  of  various  Forms  for  Boiler-construction. — Although  the 
spherical  shell  possesses  greatly  superior  strength  over  all  other  forms  of  structure, 
and  has  the  additional  advantage  of  accommodating  itself  to  the  expansive  action  of 
heat  without  distortion,  its  employment  in  boiler-construction  is  very  limited  on  account 
of  the  comparative  difficulty  of  giving  this  form  to  the  material  used.  The  property  of 
the  sphere  of  presenting  less  surface  than  any  other  body  in  proportion  to  its  content  is 
an  objection  to  its  use  in  connection  with  the  heating-surfaces  of  a  boiler,  and  its  use 
for  external  shells  would  entail  a  great  loss  of  room  in  waste  spaces.  The  ends  of 
cylindrical  shells  of  land  boilers  and  the  top  of  steam-drums  are  often  made  of  spheri- 
cal segments ;  spherical  strengthening-domes  are  sometimes  attached  to  flat  surfaces 
where  staying  by  rods  or  gussets  is  inexpedient.  The  Harrison  boiler  is  composed 
almost  entirely  of  small  cast-iron  spheres  connected  by  short  tubes. 

The  cylindrical  form  has  the  most  extensive  application  in  boiler-making.  It  pos- 
sesses next  to  the  sphere  the  greatest  strength  ;  it  is  readily  produced  of  any  required 
size  and  of  all  materials  used  in  boiler-making.  Since  with  cylindrical  forms  stays  and 
braces  can  be  dispensed  with,  their  use  makes  a  boiler  accessible  and  cheapens  its 
construction. 

The  use  of  flat  surfaces  is  in  many  cases  unavoidable  for  an  economic  utilization  of 
the  space  allowed  and  for  the  proper  arrangement  of  the  interior  parts  of  a  boiler.  The 


SBC.  7.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  139 

heads  of  the  shell,  the  tube-sheets,  and  the  back  of  the  back-connection  are  always 
made  flat  in  cylindrical  marine  boilers  of  the  usual  type.  When  the  steam-pressure  is 
not  to  exceed  45  Ibs.  per  square  inch  above  the  atmosphere  the  outer  shell  of  marine 
boilers  is  generally  made  box-shaped,  with  square  sides  and  the  corners  more  or  less 
rounded ;  by  using  this  form  of  boiler  the  space  in  a  vessel  allotted  to  it  can  be  most 
fully  utilized,  and  the  proportions  of  the  furnaces  can  also  be  more  satisfactorily 
arranged  than  with  the  cylindrical  boiler.  On  this  account,  in  boilers  designed  to  carry 
steam  of  high  pressure,  especially  in  locomotive  boilers,  the  front  part,  containing  the 
furnace,  is  often  made  square  below  and  semi-cylindrical  on  top,  while  the  body  of  the 
boiler,  containing  the  flues  or  tubes,  is  made  a  complete  cylinder ;  or  sometimes  the 
whole  boiler  is  made  oval  in  shape. 

7.  Factor  of  Safety. — All  parts  of  a  boiler  must  possess  equal  strength.  The 
dimensions  of  the  various  parts  of  a  boiler  must  not  be  calculated  by  applying  a  uni- 
form factor  of  safety  to  the  formulas  expressing  the  strength  of  the  respective  shapes, 
but  account  must  be  taken  of  the  continual  waste  taking  place  in  all  parts  of  a  boiler  in 
consequence  of  external  and  internal  corrosion  and  the  wasting  effect  of  the  intense 
heat  produced  in  the  furnace.  Since  the  deterioration  resulting  from  these  causes 
affects  different  parts  and  forms  in  a  different  degree,  the  allowance  of  additional  thick- 
ness of  metal  to  be  made  on  this  account  must  vary  accordingly.  Care  must  also  be 
taken  that  such  parts  as  cannot  be  readily  replaced  or  repaired  be  proportioned  with 
an  extra  large  margin  of  strength. 

The  plates  of  boilers  must  be  proportioned  and  stayed  not  only  with  regard  to 
strength,  but  sufficient  stiffness  must  be  given  to  them  to  prevent  changes  of  shape 
under  pressure.  A  change  of  shape  in  one  direction  by  pressure,  and  returning  again 
to  its  original  position  when  the  pressure  is  released,  will  sooner  or  later  result  in  a 
crack.  The  same  is  true  when  braces  are  attached  in  such  a  way  that  the  sheet  is 
drawn  from  its  true  position. 

The  tensile  stress  exerted  by  the  maximum  steam-pressure  on  any  part  of  a  boiler 
should  not  exceed  one-sixth  of  its  ultimate  strength.  This  factor  of  safety  is  usually 
employed  for  parts  of  machinery  subjected  to  alternating  stresses  acting  in  opposite 
directions.  The  steam-pressure  in  a  boiler  cannot  be  considered  as  a  quiescent  load,  on 
account  of  the  constantly  occurring,  and  sometimes  considerable,  fluctuations  of  pressure 
due  to  various  causes  ;  besides,  the  different  parts  of  a  boiler  are  subjected  to  continual 
expansions  and  contractions  owing  to  changes  of  temperature,  the  effect  of  which  can- 
not be  calculated,  but  is  very  marked  under  certain  conditions.  The  force  exerted  by 
expansion  or  contraction  as  the  effect  of  change  of  temperature  is  equal  to  that  which 


140  STEAM  BOILERS. 


CHAP.  VII. 


would  be  required  to  elongate  or  compress  the  material  to  the  same  extent  by  mechani- 
cal means.  The  linear  expansion  of  ordinary  wrought-iron  plates  is  .0000064  of  their 
length  for  each  degree  Fahrenheit  of  increase  of  temperature,  and  the  same  elongation 
is  produced  by  a  stress  of  about  150  Ibs.  per  square  inch  of  section  of  metal.  It  must 
be  observed  that  this  stress  produced  by  increase  of  temperature  is  independent  of  the 
sectional  area  of  the  plate,  and  if  the  expansion  or  contraction  of  the  plate  is  not 
allowed  to  go  on  freely  a  corresponding  stress  will  be  exerted  on  the  metal  by  a  change 
of  temperature. 

In  case  the  substitution  of  mild,  ductile  cast-steel  for  piled  wrought-iron  plates  for 
boilers  should  be  warranted  by  further  practice,  it  may  be  considered  safe  to  decrease 
the  factor  of  safety  to  four,  on  account  of  the  greater  homogeneousness  and  uniformity 
of  quality  of  the  steel  plates  rolled  from  single  ingots. 

It  must  be  remembered  that  the  strength  of  any  structure  is  to  be  measured  by  that 
of  its  weakest  part,  which  in  the  case  of  boilers  is  the  joint  where  the  sheets  are  con- 
nected. The  strength  of  various  forms  of  joint  employed  in  boiler-making  will  be  dis- 
cussed in  the  next  chapter. 

The  '  Eevised  Statutes  of  the  United  States '  prescribe  the  following  rule  regarding 
the  factor  of  safety  to  be  employed  in  determining  the  strength  of  marine  boilers : 
"  Section  4433.  The  working  steam -pressure  allowable  on  boilers  constructed  of  plates 
inspected  as  required  by  this  title,  when  single-riveted,  shall  not  produce  a  strain  to 
exceed  one-sixth  of  the  tensile  strength  of  the  iron  or  steel  plates  of  which  such  boilers 
are  constructed  ;  but  where  the  longitudinal  laps  of  the  cylindrical  parts  of  such  boilers 
are  double-riveted,  and  the  rivet-holes  for  such  boilers  have  been  fairly  drilled  instead 
of  punched,  an  addition  of  twenty  per  centum  to  the  working-pressure  provided  for 
single-riveting  may  be  allowed :  Provided,  That  all  other  parts  of  such  boilers  shall  cor- 
respond in  strength  to  the  additional  allowances  so  made,  and  no  split-calking  shall  in 
any  case  be  permitted." 

In  the  case  of  large  cylindrical  flues  subjected  to  compression  the  factor  of  safety 
should  be  increased  to  eight  at  least  when  Fairbairn'  s  formula  is  employed  ;  in  addition 
to  this  the  thickness  of  the  metal  must  be  increased  tt  or  i  incn  to  allow  for  corrosion 
and  other  wasting  influences.  To  allow  for  corrosive  and  other  destructive  influences 
in  the  case  of  the  rectangular  boiler,  the  lower  parts  of  the  outer  shell,  the  water- 
legs,  and  the  bottom  of  the  back-connections  are  generally  made  from  \  to  •£$  inch 
thicker  than  the  other  parts  of  the  shell ;  the  parts  exposed  to  an  intense  heat  are  less 
increased  in  thickness,  on  account  of  the  liability  of  thick  plates  to  blistering ;  there- 
fore the  furnaces  and  the  sides,  tops,  and  fronts  of  the  back-connections  receive  an  in- 


SEC.  8.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  141 


crease  of  ^  *&<&  O10^7  5  tne  tube-sheets,  on  the  contrary,  are  still  further  increased  in 
thickness,  in  order  to  allow  for  the  loss  of  stiffness  in  consequence  of  the  many  large 
holes  drilled  in  them,  and  to  give  a  sufficient  bearing-surface  to  the  tubes. 

Stays  and  braces  are  generally  proportioned  to  bear  a  strain  of  from  4,000  to  5,000 
Ibs.  per  square  inch  of  section  ;  a  more  rational  method  of  proportioning  them,  how- 
ever, is  to  calculate  the  required  cross-section,  according  to  the  pressure  on  the  surface 
which  they  have  to  support,  using  six  as  a  factor  of  safety,  and  adding  a  certain  amount 
to  the  thickness  or  diameter  thus  found  to  allow  for  corrosion.  Generally  it  will  be 
sufficient  to  add  i  inch  to  the  thickness  required  for  strength  ;  but  near  the  water-level 
and  in  narrow  water-spaces  the  increase  in  thickness  has  to  be  greater.  Welded  parts 
must  likewise  receive  an  additional  increase,  since  the  metal  is  there  more  easily  at- 
tacked by  corrosion  and  the  strength  of  welded  joints  varies  greatly. 

8.  Drawings  and  Specifications.  —  After  the  dimensions  and  the  general  shape 
and  arrangement  of  a  boiler  have  been  decided  upon,  the  exact  forms  and  proportions 
of  the  various  parts  can  be  most  advantageously  determined  by  making  a  drawing  of 
the  boiler,  showing  front  and  side  elevations,  and  a  plan,  including  such  full  or  partial 
sectional  views  as  are  required  for  a  complete  illustration  of  every  part  of  the  boiler. 
On  the  drawing  all  dimensions  necessary  to  guide  the  boiler-maker  in  the  construction 
of  the  boiler  must  be  plainly  marked,  including  the  thickness  of  the  sheets,  the  size  and 
position  of  all  openings  for  steam,  feed  and  blow-off  pipe  connections,  and  for  man 
and  handhole  plates,  safety-valves,  etc.,  the  position  and  attachment  of  the  braces  and 
stays,  and  the  location  and  form  of  the  principal  seams.  This  drawing  is  generally 
made  to  a  scale  of  I  inch  or  \\  inches  to  the  foot.  Drawings  on  a  larger  scale  are  made 
to  show  in  detail  the  devices  adopted  for  bracing  different  parts  of  the  boiler,  and  the 
various  attachments  of  the  boiler,  as  well  as  the  arrangement  of  the  uptake  and  chim- 
ney. In  order  to  determine  all  these  details  intelligently  it  is  advisable  to  lay  down  a 
general  plan  on  a  scale  of  1  inch  or  f  inch  to  a  foot,  showing  the  location  of  the  boilers 
in  the  vessel  with  regard  to  floors,  keelsons,  decks,  beams,  masts,  and  bulkheads,  the 
mode  of  securing  the  boilers,  their  connections  and  attachments,  the  position  of  valves 
and  pipes,  also  the  ventilators,  doors,  stairs,  ash-hoisters,  and  other  arrangements  con- 
nected with  the  fire-room  and  used  in  the  manipulation  of  the  boilers. 

When  the  boilers  are  to  be  built  by  contract  specifications  are  written,  giving  such 
instructions  regarding  Ihe  construction  of  the  boiler  as  have  not  been  illustrated  with 
sufficient  clearness  in  the  drawings  ;  it  is  necessary  to  specify  distinctly  the  quality  of 
the  material  to  be  used  foi  different  parts  of  the  boiler,  and  the  workmanship.  Speci- 
mens of  specifications  are  appended  to  this  chapter.  - 


142  STEAM  BOILERS.  CHAP.  VII. 

The  sheets  are  ordered  from  the  maimfacturer  as  nearly  as  possible  of  the  shape  and 
size  required,  proper  allowances  being  made  for  laps  and  flanging  and  for  planing  the 
sides  and  ends. 

A  list  is  made  of  all  sheets  required,  showing  their  dimensions,  their  weight,  and  the 
part  of  the  boiler  for  which  they  are  to  be  used  ;  a  sketch,  showing  the  exact  shape  and 
dimensions  of  all  sheets  that  are  not  rectangular  or  circular,  accompanies  this  list.  In 
laying  off  the  size  of  the  sheets  care  must  be  taken  to  get  as  few  seams  as  possible  in 
contact  with  the  fire,  and  to  get  them  in  the  most  convenient  position  for  riveting  and 
accessible  for  calking.  The  greatest  tensile  stress  on  all  sheets  must  come  in  the  direc- 
tion of  the  fibre  ;  therefore  cylindrical  shells  must  be  made  with  the  fibre  of  the  sheets 
running  around  them.  Since  the  joints  are  the  weakest  and  most  troublesome  parts  of 
a  boiler,  it  is  advantageous,  with  regard  to  economy  and  strength,  to  make  the  sheets 
as  large  as  possible. 

9.  Specifications  for  Boilers  for  U.  S.  Steam-sloop  "  Lackawanna,"  refe- 
rence being  had  to  the  accompanying  Drawings  (Plates  VI.  and  VII.)— 
There  are  to  be  three  vertical  tubular  boilers,  containing  an  aggregate  grate-surface  of 
273  square  feet  and  a  total  heating-surface  of  8, 980  .square  feet.  The  two  main  boilers 
are  to  be  made  right  and  left ;  the  one  for  the  starboard  side  of  the  ship  is  to  be  25  feet 
long  and  to  have  seven  furnaces  ;  the  opposite  boiler  is  to  be  21  feet  6  inches  long  and 
to  have  six  fxirnaces  ;  the  other,  or  auxiliary,  boiler  is  to  have  one  furnace,  and  is  to  be 
placed  aft  of  the  six-furnace  boiler,  and  is  to  be  4  feet  long. 

Extreme  height  of  boilers,  exclusive  of  steam-drums,  to  be  9  feet  5  inches. 

Extreme  depth  of  boilers  at  furnaces,  10  feet  3  inches ;  at  top  of  shell,  11  feet  9 
inches. 

Each  main  boiler  is  to  have  a  steam-drum  extending  2  feet  9  inches  above  the  top  of 
shell.  Each  furnace  is  to  be  made  with  an  independent  combustion-chamber,  which 
communicates  through  a  tube-box  containing  310  tubes  with  a  front-connection,  and 
unites  with  the  others  in  a  common  uptake  which  is  to  have  a  calorimeter  equal  to  that 
of  all  the  tube-boxes. 

Material. — All  the  parts  of  the  boilers,  except  the  tubes,  are  to  be  made  of  the  very 
best  American  charcoal-iron. 

Water-legs. — The  boilers  are  to  be  made  with  water-legs,  which  are  to  enclose  water- 
spaces  6  inclies  wide,  including  the  thickness  of  metal ;  they  are  to  be  made  of  the  best 
flange  iron  •&  inch  thick  ;  the  bottom  plate  of  each  to  be  of  one  sheet,  and  to  be  made 
to  lap  outside  the  vertical  plates  forming  the  leg. 

Shell  of  Boilers. — The  bottom  of  shell  at  back  part  of  boilers  to  be  ^  inch  thick 


SEC.  9.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  143 

and  to  extend  above  the  turn  to  the  sides.    All  other  parts  of  the  shell  to  be  ^  inch 
thick. 

Furnaces. — Each  furnace  is  to  be  3  feet  wide  and  6  feet  6  inches  long  on  the  grates. 
The  crown  of  each  furnace  is  to  be  f  inch  thick,  and  made  of  one  sheet  extending  on 
each  side  below  the  grate-bars. 

Connections  and  Tube-boxes. — The  front-heads  of  furnaces  and  back-heads  of 
back-connections  are  to  be  made  of  the  best  flange-iron  f  inch  thick ;  sides  and  top 
of  back-connections  f  inch  thick,  and  bottom  -^  inch  thick;  the  sides  of  tube- 
boxes  f  inch  thick  ;  front-connections  and  uptake  to  be  f  inch  thick,  to  be  of  the  best 
flange-iron. 

Tube-sheets  to  be  f  inch  thick,  of  the  best  flange-iron.  Water-spaces  between  the 
tube-boxes,  front  and  back  connections,  to  be  6  inches  wide,  including  the  thickness  of 
metal. 

The  tubes  are  to  be  made  of  drawn  brass,  to  be  2  inches  external  diameter  and  33J 
inches  long,  and  to  be  of  No.  13  wire-gauge  thickness. 

Bracing. — The  top  and  side  of  the  shell  of  boiler  above  the  tube-boxes  to  be  stiffened 
by  T-iron  3£"  x  3J"  X  f  *,  placed  every  12  inches,  to  which  the  braces  are  to  be  attached. 
Each  flange  of  the  T-iron  is  to  be  riveted  to  the  shell  every  four  (4)  inches,  and  the  rivets 
so  placed  as  to  alternate  with  each  other.  The  braces  are  to  be  not  over  12  inches  apart, 
and  to  be  coupled  to  diagonals,  which  are  to  be  attached  to  the  T-iron  by  bolts  and  nuts 
placed  not  over  12  inches  between  centres ;  braces  to  be  1£*  diameter ;  diagonals  to 
be  double,  of  rectangular  section  2*  X  f ",  and  secured  by  bolts  1J*  diameter.  All  flat 
spaces  not  stiffened  by  T-iron  to  be  braced  every  8  inches  by  socket-bolts  of  1"  diameter. 
Crown  of  furnaces  to  be  thoroughly  braced.  Care  is  to  be  taken  that  the  strength  of 
bracing  herein  specified  is  to  be  carried  out  in  all  the  diagonals,  angle  and  T-irons,  and 
their  rivets  and  attachments,  and  in  the  welding,  so  that  no  parts  are  left  more  weakly 
braced  than  herein  specified. 

Riveting. — All  seams  not  in  contact  with  the  fire  to  be  double-riveted,  and  the  rivets 
to  be  staggered. 

Seams. — All  seams  to  be  calked  on  both  sides  when  practicable,  and  no  acids  are  to 
be  used  in  forming  them,  nor  any  fitting  pieces  to  be  inserted. 

Manholes. — Each  boiler  is  to  be  provided  with  two  manholes,  12*  X  15*  diameter, 
opening  into  the  steam-room,  one  on  each  end  of  the  main  boilers,  placed  on  the  front 
side,  and  one  in  the  front  side  of  the  auxiliary  boiler. 

Manholes,  12'  x  15"  diameter,  will  also  be  placed  in  the  spandrels  of  the  furnaces. 
Each  manhole  is  to  have  around  it  on  the  inside  a  wrought-iron  band,  I  inch  thick  and 


144  STEAM  BOILERS.  CHAP.  VEL 

4  inches  wide,  double-riveted  to  the  shell ;  inner  row  of  rivets  countersunk  flush  on 
both  sides. 

Manhole-cotters. — The  manholes  to  be  provided  with  cast-iron  covers,  the  joints  of 
which  are  to  be  faced.  The  plates  to  be  secured  in  place  by  wrought-iron  cross-bars 
and  bolts. 

Handholes. — Each  boiler  is  to  have  a  handhole  near  the  bottom  of  each  leg  at  each 
end.  Openings  to  be  elliptical,  with  diameters  of  3"  and  5",  and  to  be  fitted  with  cast- 
iron  plates,  the  joints  of  which  are  to  be  faced  ;  bars,  bolts,  and  rivets  to  be  of  wrought- 
iron. 

The  Furnace-doors  and  Grate-bars  are  to  be  furnished  by  the  Government  and  to 
be  properly  fitted  in  place  by  the  contractors. 

Uptake-doors  to  be  of  wrought-iron,  double-shell,  and  fitted  with  the  proper  hinges 
and  latches,  and  to  be  filled  with  some  approved  non-conducting  substance. 

Ashpit-doors  to  be  made  of  wrought-iron,  \"  thick,  with  a  flange  f"  deep  all  around  ; 
to  be  well  fitted  for  closing  the  ashpit,  and  arranged  to  hang  by  proper  hooks  to  the 
uptake-doors  when  not  in  use.  • 

1O.  Extract  from  Specifications  for  Engines  of  U.  S.  S.  "  Miantonomoh." 
(Plate  VIII.) 

Boilers  and  Attachments. — There  are  to  be  six  return  horizontal  tubular  boilers, 
placed  forward  of  the  engines,  three  on  each  side  of  the  vessel,  with  the  fire-room  run- 
ning fore  and  aft  between  them. 

There  is  to  be  one  chimney  in  vertical  line  over  the  keel,  connecting  with  an  uptake 
common  to  all  the  boilers. 

The  boilers  are  to  be  constructed  of  the  best  American  charcoal  flange-iron ;  all 
seams  not  in  contact  with  the  fire  to  be  double-riveted.  All  the  plates  to  be  planed  on 
the  edges,  the  seams  to  be  butt-jointed  and  covered  with  butt-straps  of  the  same  thick- 
ness as  the  plates  with  which  they  are  in  contact ;  all  to  be  calked  perfectly  tight. 

Each  boiler  is  to  be  12  feet  external  diameter  and  10  feet  in  length,  to  have  three 
cylindrical  furnaces,  36  inches  internal  diameter,  projecting  6  inches  from  front  of  boiler 
and  extending  to  the  back-connections. 

Grate-surface. — Each  furnace  is  to  have  a  grate  36  inches  wide  and  84  inches  long, 
or  21  square  feet,  aggregating  378  square  feet  in  the  six  boilers. 

Grate-bars  to  be  double,  in  two  lengths,  f  inch  apart,  f  inch  thick  at  top,  ^  inch  at 
bottom,  4  inches  deep  at  centre  and  2  inches  at  ends. 

Tubes. — Each  boiler  is  to  contain  197  drawn-brass  tubes,  3  inches  external  diameter 
and  7  feet  3  inches  long,  No.  12  wire-gauge  thickness. 


SEC.  10.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  145 

» 

Shell  to  be  formed  of  plates  f  inch  thick ;  joints  to  be  butted  and  strapped,  and  to 
be  double-riveted  each  side  of  seams. 

Heads. — The  front  and  back  heads  to  be  £  inch  thick,  each  composed  of  three  plates 
making  two  horizontal  joints,  planed  and  butted ;  the  straps  to  be  £  inch  thick  and 
9£  inches  wide,  double-riveted  each  side. 

Bracing. — The  heads  will  be  braced  by  rods,  If  inches  in  diameter,  placed  12  inches 
between  centres ;  the  ends  of  rods  to  be  made  with  jaws  and  coupled  to  stay -plates 
at  each  end  by  a  wrought -iron  bolt  If  inches  in  diameter.  Stay-plates  to  be  of  the  best 
iron,  f  inch  thick,  and  secured  to  boiler  by  a  flange  2f  inches  wide  and  an  angle-iron  3 
by  3£  inches.  The  stay-plates  to  be  made  with  lugs  6  inches  in  diameter,  leaving  open- 
ings for  the  removal  of  the  braces. 

Furnaces. — The  furnaces  are  to  be  made  of  the  very  best  iron,  £  inch  thick.  Each 
furnace  is  to  be  formed  of  three  cylindrical  sections,  36  inches  internal  diameter,  butted 
and  strapped,  flanged  on  the  ends,  and  riveted  to  each  other  with  a  welt,  f  inch  thick, 
between  them.  The  furnaces  to  be  double-riveted  at  their  junctions  with  the  front- 
heads. 

The  Back-connections  are  to  be  27  inches  deep  and  made  as  shown  in  the  drawings ; 
side  and  back  plates  to  be  of  £-inch  iron.  The  side  and  back  heads  to  be  stayed  by 
socket-rivets  1  inch  in  diameter  and  spaced  not  over  7  inches  from  centre  to  centre. 

The  Tube-sheets  are  to  be  £  inch  thick.  The  centre  tube-sheets  are  to  be  accur- 
ately drilled  for  63  tubes ;  the  two  outer  tube-sheets  to  be  accurately  drilled  for  67 
tubes  in  each.  The  tubes  are  to  be  spaced  horizontally  and  vertically  4  inches  between 
centres. 

Manholes. — There  are  to  be  manholes  9£  inches  by  13  inches  in  the  front-head  of 
each  boiler  in  the  outer  spandrels  above  the  furnaces,  and  in  the  lower  spandrels  be- 
tween the  furnaces,  and  a  manhole  11  by  15  inches  in  the  space  above  the  centre  furnace. 
Each  manhole  to  have  around  it  on  the  outside  a  wrought-iron  band,  1  inch  thick  and 
4  inches  wide,  double-riveted  to  shell ;  inner  row  of  rivets  countersunk  flush  on  both 
sides.  Manholes  to  be  closed  with  cast-iron  plates  and  secured  with  double  wrought- 
iron  cross-bars  and  bolts. 

The  Front-connections  and  Uptakes  are  to  be  made  with  double  shells  of  wrought- 
iron,  built  on  angle-iron  frames  ;  the  angle-iron  to  be  2J  inches  by  If  inches  ;  the  inside 
and  outside  shells  to  be  made  of  iron  weighing  respectively  5  Ibs.  and  3^  Ibs.  per  square 
foot.  The  space  between  shells  to  be  filled  with  some  non-conducting  material.  The 
uptake  at  the  connection  with  the  smoke-pipe  to  be  8  feet  3  inches  in  diameter.  The 
doors  are  to  be  made  of  wrought-iron,  double  shell,  and  fitted  with  the  proper  hinges 


146  STEAM  BOILERS.  CHAP.VH. 

and  catches  ;  outside  shell  i  inch  thick,  flanged  1  inch  deep  ;  inside  shell  J  inch  thick, 
flanges  2J  inches  deep. 

Furnace-fronts  to  be  made  with  a  cast-iron  frame  covered  with  wrought-iron  plates 
f  inch  thick,  and  having  openings  20  by  13i  inches  for  furnace-doors.  The  outside 
plates  to  have  twelve  air-holes  1£  inches  in  diameter,  and  the  inside  plates  to  be  per- 
forated with  250  holes  ^  inch  in  diameter. 

The  Furnace-doors  to  be  made  with  wrought-iron  fronts  i  inch  thick  and  flanged  1 
inch  deep ;  each  to  be  fitted  with  a  perforated  wrought-iron  back  and  the  necessary 
hinges  and  latches  of  wrought-iron. 

The  Ashpit-doors  to  be  made  of  wrought-iron  \  inch  thick,  flanged  1  inch  deep  ;  to 
be  well  fitted  to  close  the  ashpits,  and  arranged  to  hang  by  proper  hooks  on  uptake- 
doors  when  not  in  use. 

Saddles. — Each  boiler  is  to  rest  on  two  saddles  made  of  wrought-iron  and  properly 
secured  to  the  ship.  The  boilers  to  be  secured  to  the  saddles  by  suitable  wrought-iron 
straps  and  bolts.  The  bolts  for  straps  (which  pass  through  the  shell)  to  be  turned  and 
snugly  fitted  into  reamed  holes. 

Steam-drums. — There  are  to  be  two  steam-drums  .on  each  side,  placed  in  the  span- 
drels above  the  boilers,  each  to  be  42  inches  in  diameter  and  8  feet  6  inches  long. 
Shells  to  be  £  inch  thick,  heads  £  inch  thick.  Each  head  to  be  braced  by  ten  gussets 
equally  divided  on  the  shell ;  gussets  to  be  of  f -inch  iron,  extending  30  inches  on  the 
shell  and  11  inches  on  the  head,  and  securely  riveted  to  shell  and  head  by  angle-iron  2J 
by  2|  inches. 

Two  Superheating  Steam-pipes,  15  inches  in  diameter,  made  of  the  best  boiler-plate 
^oV  inch  thick,  are  to  be  placed  within  each  front-connection,  and  united  with  each  other 
at  forward  ends  and  to  steam-drums  placed  in  the  spandrels  above  the  boilers.  All  to 
be  of  the  best  American  charcoal-iron. 

Safety-valves.— Each  boiler  and  superheating-pipe  is  to  have  a  safety-valve  5£  inches 
in  diameter,  fitted  with  the  proper  weights  and  levers  for  a  pressure  of  80  Ibs.  of  steam. 
The  chests  to  be  of  cast-iron,  the  valves  and  seats  of  composition  ;  the  valves  to  be  con- 
nected to  copper  pipes  leading  to  the  chimney. 

Dry-pipes. — Each  boiler  is  to  have  a  sheet-brass  dry-pipe  thoroughly  tinned  and  of 
an  internal  diameter  of  7  inches  ;  the  pipe  to  be  placed  as  high  as  possible  and  extend 
nearly  the  length  of  the  boiler  ;  the  top,  for  a  distance  of  3|  feet  on  either  side  of  the 
centre  of  its  length,  to  have  holes  f  inch  in  diameter  drilled  equally  distant ;  the  aggre- 
gate area  to  be  double  the  cross-section  of  the  pipe. 

Stop-valves. — Each  boiler  is  to  have  a  composition  stop-valve  placed  on  the  back- 


SEC.  10.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  147 


head  near  the  top,  and  united  with  the  boiler  and  dry-pipe  by  flanges  llf  inches  in 
diameter  and  |f  inch  thick  ;  the  chest  to  be  not  less  than  ^  inch  thick.  The  valve  is  to 
be  6  inches  in  diameter,  and  fitted  with  a  screw-stem  made  to  torn  independently  of  the 
valve,  and  work  in  a  composition  nut  supported  by  wrought-iron  studs  on  the  covers  ; 
the  valve  to  be  operated  by  a  composition  hand-wheel  12  inches  in  diameter. 

Pipes.  —  The  stop-valves  are  to  be  connected  with  the  steam-drums  by  copper  pipes 
6  inches  internal  diameter  and  No.  16  Birmingham-gauge  thickness  ;  the  pipes  to  have 
composition  flanges,  11£  inches  in  diameter  and  }$  inch  thick,  properly  riveted  and 
brazed  on. 

Main  Stop-valves.—  There  are  to  be  two  main  steam  stop-  valves  placed  between  the 
boilers  and  the  engines  ;  they  are  to  be  connected  with  the  superheating-pipes  and  each 
other  by  pipes  12  inches  in  diameter,  and  arranged  to  close  the  steam  from  either  the 
port  or  starboard  boilers  while  the  others  are  in  use.  The  chests  are  to  be  of  cast-iron 
|  inch  thick,  flanges  If  inches  thick.  They  are  to  be  fitted  with  composition  valves  and 
seats,  the  valves  to  be  12  inches  in  diameter,  and  are  to  have  screw-stems  made  to  turn 
independently  of  the  valves  and  work  in  composition  nuts  supported  by  wrought-iron 
studs  on  the  covers  ;  the  valves  to  be  operated  by  composition  hand-wheels  20  inches  in 
diameter. 

The  Main  Steam-pipes  are  to  be  of  copper  ;  three  sections  to  be  12  inches  in  diameter 
and  of  No.  11  Birmingham-gauge  thickness,  two  sections  of  10  inches  diameter  and  No. 
14  Birmingham-gauge  thickness  ;  the  sections  connecting  with  the  throttle-  valves  to  be 
9  inches  in  diameter  and  No.  14  Birmingham-gauge  thickness  ;  the  several  sections  to 
be  united  to  each  other  and  the  valves  by  composition  flanges  £  inch  thick,  properly 
riveted  and  brazed  to  the  pipes.  All  the  steam-pipes  to  be  heavily  tinned  inside  and 
out. 

Bleeding-valve  and  Pipe.  —  There  is  to  be  a  copper  pipe,  with  stop-valve,  of  4  inches 
in  diameter,  leading  from  the  steam-pipe  to  the  top  of  the  condenser  for  bleeder. 

Check  and  Slow  Valves.—  Each  boiler  is  to  have  a  check  feed-  valve,  2f  inches  in  dia- 
meter, enclosed  in  a  chest  having  two  stop-  valves  of  the  same  diameter,  that  may  be 
closed  from  the  boiler  and  feed-pipe  ;  the  valve  and  chest  to  be  of  brass  and  made  with 
flanges  6J  inches  in  diameter,  £  inch  thick,  for  connecting  with  feed-pipes  and  boilers. 
Each  boiler  is  to  have  a  bottom  blow-  valve  of  brass  2£  inches  in  diameter,  also  a  sur- 
face blow-  valve  2  inches  in  diameter,  all  connected  by  suitable  pipes  to  the  sea-valves 
on  the  ship. 

The  Main  Feed  and  Slow  Pipes  to  be  made  in  sections  not  exceeding  12  feet  in 
length,  and  are  to  be  of  drawn-brass  tubes,  3f  inches  inside  diameter,  of  No.  8  Binning- 


148  STEAM  BOILERS.  CHAP.  V1L 

ham-gauge  thickness  ;  the  branches  to  be  3  inches  inside  diameter,  of  No.  9  Birmingham 
gauge ;  the  pipes  to  be  fitted  with  composition  flanges  and  elbows  for  uniting  the 
sections,  and  are  to  be  expanded  in  and  sweated  to  them ;  the  interior  of  pipes  to  be 
well  tinned. 

Gauge-cocks. — Each  boiler  is  to  have  a  combination  gauge,  which  shall  include  a 
glass  tube  of  18  inches  exposed  length,  and  four  cocks  placed  6  inches  apart,  also  drip- 
pan  and  pipe  ;  the  lowest  cock  to  line  with  the  bottom  of  glass  tube,  and  placed  to  show 
the  level  of  the  water  at  the  highest  heating-surface. 

Salinometers. — There  are  to  be  six  of  Fithian's  salinometer-pots,  fitted  in  such  a 
manner  as  to  be  easily  accessible. 

Steam-whistle. —  A  large,  finished  steam- whistle  of  brass  is  to  be  conveniently  placed 
above  deck,  with  copper  pipe  and  cock  connecting  to  boilers. 

Test. — Before  being  placed  in  the  vessel  all  the  boilers  are  to  be  subjected  to  a  pres- 
sure of  120  Ibs.  to  the  square  inch,  which  is  to  be  obtained  by  filling  the  boilers  quite 
full  of  water  and  lighting  a  fire  in  the  furnaces,  producing  the  pressure  by  the  expan- 
sion of  the  water.  The  boilers,  after  completion,  to  be  painted  inside  and  out  with  two 
coats  of  brown  zinc-paint. 

Covering  for  Boilers. — After  the  boilers  are  in  the  vessel  the  entire  shell  and  backs 
of  the  same  are  to  be  covered  with  a  casing  of  galvanized  iron,  enclosing  an  air-space  of 
H  inches  between  the  boilers  and  casing  ;  the  sections  of  the  casing  to  be  substantially 
connected  with  each  other,  and  in  such  a  manner  that  they  may  easily  be  removed  and 
replaced,  and  the  joints  made  perfectly  air-tight.  The  casing  to  be  made  with  suitable 
openings  and  covers  over  man  and  handholes  and  braces  required  to  be  removed  from 
the  outside.  The  casing  to  be  covered  with  two  coats  of  brown  zinc-paint. 

Ventilators  18  inches  in  diameter  are  to  fitted  for  the  fire-room  ;  they  will  extend 
below  the  deck  to  within  8  feet  of  the  fire-room  floor,  and  to  be  bell-mouthed  at  lower 
end.  The  portion  above  deck  will  be  secured  to  deck  by  screwed  eye-bolts  passing 
through  a  flange  and  tapped  into  the  rings  around  the  holes  through  deck-plating ;  they 
are  to  have  movable  hoods,  capable  of  being  worked  from  fire-room,  and  will  be  made  of 
iron  No.  11  wire-gauge  thick.  The  forward  ventilators  are  to  be  arranged  for  hoisting 
ashes  through  them  from  deck  by  means  of  blocks  and  pulleys  ;  to  be  strengthened  with 
six  strips  of  bar-iron  placed  vertically  in  the  interior.  These  ventilators  to  have  a  side- 
door  for  passing  the  ash-buckets  through. 

11.  Specification  of  Boilers  (Iron  Shells)  for  Vessels  of  the  English 
Navy.— Specification  of  certain  particulars  to  be  strictly  observed  in  the  construction 
of set  of  marine  boilers,  with  superheaters,  of  the  collective  indicated  power 


SEC.  11.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  149 

of  horses,  suitable  for  vessels  of  the class.     They  are  to  be  delivered 

complete  by  the ,  18 .. 

Boilers. — The  boilers  to  be  tubular,  capable  of  carrying  steam  of Ibs.  to  the 

square  inch,  and  to  be  proved  by  water-pressure  to .  to  the  square  inch. 

They  are  to  be  constructed  in  separate  parts,  in  accordance  with  the  form  and 

dimensions  shown  upon  the  accompanying  tracing. 

Furnaces. — There  are  to  be .  furnaces  of  the  dimensions  given  on  the  tracing. 

To  admit  of  bituminous  coal  as  well  as  Welsh  coal  being  burned  effectively,  perforated 
bridges  are  to  be  fitted,  with  means  of  regulating  the  supply  of  air  through  them  to  any 
degree  of  opening.  The  aggregate  area  of  the  perforations  in  the  bridges  to  be  not  less 
than  3  square  inches  per  square  foot  of  fire-grate  for  admission  of  air  to  the  combustion- 
chambers.  The  furnace-doors  to  be  fitted  with  internal  and  external  screen-plates,  per- 
forated with  a  few  holes  to  keep  the  doors  cool,  and  means  to  be  provided  for  keeping 
them  open  in  a  sea-way. 

The  furnace-bars  to  be  of  wrought-iron,  3£  inches  deep  by  1£  inches  wide,  and  to  be 
made  in lengths.  The  length  of  fire-grate  to  be feet inches. 

Boiler-plates,  etc. — The  tube-plates,  the  uptakes,  the  furnaces,  and  the  combustion- 
chambers,  with  the  angle-iron  and  rivets  in  these  parts,  and  all  screwed  stays,  are  to  be 
of  Low  Moor,  Bowling,  or  Farnley  iron,  and  all  other  parts  of  BB  Staffordshire  or  other 
iron  of  equal  quality.  The  minimum  thickness  of  the  boiler-plates  to  be  as  follows : 

tube-plates; inch  ;  uptakes  and  bottom  of  shells, inch  ;  bottoms  of  furnaces, 

inch  ;  upper  and  lower  parts  of  fronts, inch  ;  and  all  other  parts,  „  _  inch. 

The  bottom  plates  of  the  shells  to  be  double-riveted  throughout.  All  the  plates  of  the 
boilers  to  be  lap- jointed,  excepting  the  lower  parts  of  the  fronts,  which  are  to  be  lap- 
welded. 

Tests  of  Plates. — All  plates  (with  the  exception  of  Low  Moor,  Bowling,  or  Farnley 
plates,  which  will  not  be  tested)  must  be  capable  of  standing  the  following  tests : 

Tensile  strain  per  square  inch. 

Lengthways 21  tons. 

Crossways 18     " 

Forge-test  (hot). 

Plates  to  admit  of  being  bent  hot,  without  fracture,  to  the  following  angles : 

Lengthways  of  the  grain 125  degrees. 

Across . .  .  100        " 


150 


STEAM  BOILERS. 


CHAP.  VII. 


Forge-test  (cold). 
Plates  to  admit  of  being  bent  cold,  without  fracture,  to  the  following  angles : 


Thickness  of  plate. 

With  the  grain. 

Across  the  grain. 

Through  an  angle  of 

Through  an  angle  of 

i        inch. 

15     degrees. 

5     degrees. 

H 

15 

5 

I 

20 

7* 

H 

20 

7i 

f 

22^ 

10 

H 

25 

10 

1 

27^ 

12* 

* 

3° 

«* 

i 

35 

15 

7 

44 

i7* 

1 

5° 

20 

A 

60 

2S 

<  ' 

i    ' 

70 

30 

Tests  of  Tee-irons  and  Angle-irons. — Tensile  strain  per  square  inch  with  the  grain, 
for  every  description,  21  tons. 

The  ductility  and  other  qualities  of  the  iron  should  be  such  as  to  admit  of  its  being 
bent  hot  and  cold  in  the  following  manner,  without  fracture : 


ANGLE-IKON. 

Forge-test  (hot). 
Angle-iron  should  be  tested  hot  by  being  bent  thus  : 

Fig.  lO.o 


Fig. 11. a 


and  also  by  being  flattened  thus : 
and  the  end  bent  over  thus  : 


Fig.  12. a 


V 


Fig.13.« 


Fig. 14.« 


SEC.  11. 


DESIGN,  DRAWINGS,  AND  SPECIFICATIONS. 


151 


Forge-test  (cold). 

Angle-iron  should  also  be  notched  and  broken  across  cold  to  show  . 
the  quality  of  the  iron  ;  and  one  flange  should  be  cut  off  and  bent  cold, 
thus:  Fig.ts.a 

TEE-IKON. 

Forge-test  (hot). 

Tee-iron  should  be  tested  hot  by  being  bent  thus  • 
Forge-test  (cold). 

The  cold  test  for  tee-iron  should  be  similar  to  that  for 
angle-iron. 

Tests  of  Stays  and  Rivets. — Samples  of  angle,  tee,  and 
bar  iron  for  testing  are  to  be  selected  from  quantities  of  two  tons  or  portion  of  two 
tons  weight. 

Bar-stays,  Yorkshire  iron  screwed  stays,  and  rivets  are  to  be  capable  of  standing  a 
tensile  strain  per  square  inch  of  21  tons. 

Boiler --tubes. — The  tubes  are  to  be  of  brass,  solid-drawn  (with  the  exception  of  the 
stay  tubes,  which  are  to  be  of  Low  Moor,  Bowling,  or  Farnley  iron),  and  are  to  con- 
tain not  less  than  68  per  cent,  of  best  selected  copper. 

The  total  number  of  tubes  (including  stay -tubes)  is  to  be ,  their  mean  thickness 

to  be  not  less  than  No.  wire  gauge,  their  external  diameter  to  be  not  less  than 

inches,  and  their  length,  outside  the  tube-plates,  to  be feet  inches. 

The  stay-tubes  are  to  be  not  less  than _  inch  in  thickness. 

Test  of  Tubes. — Samples  of  tubes,  weighing  at  least  10  Ibs.,  selected  by  the  boiler 
overseer,  are  to  be  forwarded  by  the  contractors  to  Portsmouth  Dockyard,  there  to  be 
subjected  to  such  tests  as  their  Lordships  may  direct.  Each  of  the  tubes  is  to  be  tested 
by  water-pressure  separately  to  300  Ibs.  per  square  inch  in  the  presence  of  the  boiler 
overseer. 

Manholes  and  Mudholes  of  Boilers. — In  the  manufacture  of  the  boilers  care  is  to 
be  taken  to  have  sufficient  room  for  manholes  for  the  purpose  of  cleaning  and  repairing 
the  furnaces.  All  manholes  and  mudholes  of  the  boilers  to  have  stiffening-rings.  The 
doors  to  be  of  wrought-iron,  and  to  be  placed  on  the  inside  of  the  boilers.  The  manhole- 
frames  on  the  tops  of  the  boilers  to  be  raised  sufficiently  to  clear  the  lagging  of  the 
boilers. 

Stays  of  Boilers. — The  stays  are  to  be  arranged  on  an  approved  plan  so  as  to  admit 


152  STEAM  BOILERS.  CHAP.  VII. 

of  easy  access  to  the  internal  parts  of  the  boilers.  Tee-irons  to  be  attached  to  the  shells 
of  the  boilers  for  the  purpose  of  securing  the  long  stays  ;  the  rivets  or  bolts  for  securing 
the  stays  to  be  at  least  25  per  cent,  stronger  than  the  stays,  and  all  holes  for  such  rivets 
or  bolts  to  be  drilled.  Palm-stays  are  to  be  forged  from  the  solid  where  practicable. 
The  screwed  stays  to  be  nutted  on  all  flat  surfaces.  The  maximum  strain  on  the  stays 
at  the  working  pressure  must  not  exceed  5,000  Ibs.  per  square  inch  of  section  at  the 
bottom  of  the  thread. 

Circulating -plates. — Circulating-plates  are  to  be  placed  in  proper  positions  to  aid  in 
the  circulation  of  the  water,  for  which  detail  drawings  will  be  supplied  to  the  contractor. 

Zinc  Blocks. — Zinc  blocks  as  required  are  to  be  supplied  and  suspended  in  each 
boiler  for  the  purpose  of  preventing  corrosion.  A  tracing  showing  the  proposed  ar- 
rangement of  the  blocks  to  be  submitted  for  approval. 

Superheaters. — The  superheaters  to  be  of  the  form  and  dimensions  shown  upon  the 

tracing,  and  to  be  proved  to Ibs.  to  the  square  inch  by  water-pressure.     The  tubes 

are  to  be  of  wrought-iron,  Low  Moor,  Bowling,  or  Farnley,  and  not  less  than  _ inch 

thick.     Their  length  to  be feet inches,  their  diameter  to  be inches,  and 

their  total  number 

Drawings. — Before  the  work  is  put  in  hand  detail  drawings  with  figured  dimensions 
of  the  boilers  and  superheaters  are  to  be  submitted  for  approval.  The  drawings  are  to 
be  made  on  tracing-cloth,  to  a  scale  of  not  less  than  1  inch  to  the  foot,  and  are  to  give 
full  particulars  of  the  mode  of  staying  the  boilers  and  superheaters,  and  also  full  details 
of  the  furnace  frames  and  doors,  perforated  bridges,  etc.  A  duplicate  of  the  approved 
drawings  to  be  furnished  for  the  guidance  of  the  boiler  overseer. 

In  General. — No  holes,  with  the  exception  of  the  manholes  and  mudholes,  are  to 
be  cut,  but  the  positions  of  the  stop  and  safety  valves,  as  indicated  on  the  tracing,  are 
to  be  kept  clear  of  stays  and  seams. 

Dampers  are  to  be  fitted  to  the  mouth  of  every  ashpit,  and  external  plates  to  be 
fixed  to  the  fronts  of  the  smoke-box  doors.  The  threads  of  all  nuts,  screws,  studs,  etc., 
used  in  the  construction  of  the  boilers  and  superheaters  are  to  agree  with  the  threads 
used  in  Her  Majesty's  service.  Particulars  of  these,  together  with  any  additional  par- 
ticulars relating  to  the  perforated  bridges,  etc.,  will,  on  application,  be  furnished  to  the 
contractors. 

Spare  Gear. — The  following  articles  of  spare  gear  to  be  supplied : 

Boiler-tubes one-tenth  of  the  whole  number. 

Ferrules  for  boiler- tubes one  set  for  the  fire-box  end  of  each  boiler. 

Stay-tubes  with  nuts  complete one  set  for  each  boiler. 


SBC.  11.  DESIGN,  DRAWINGS,  AND  SPECIFICATIONS.  153 

Tap  and  die  with  suitable  wrenches  for  stay-tubes one  each. 

Superheater-tubes  (including  stay-tubes). 

Furnace-bars one-half  set  for  each  furnace. 

Bearing-bars sets  for         furnaces. 

Screwed  stays  for  boilers  (one  size  larger  than  required  when  new)  . .  .the  whole  number. 
Tap  and  die  for  the  above,  with  suitable  wrenches one  each. 

Supervision. — The  boilers  and  superheaters  will  be  subject  to  the  supervision  of  an 
overseer,  who  will  be  directed  to  attend  on  the  premises  of  the  contractors  during  the 
progress  of  the  work,  to  examine  the  materials  and  workmanship  used  in  their  construc- 
tion and  to  witness  the  prescribed  tests.  The  extent  of  supervision  is  described  on  the 
attached  paper  extracted  from  Admiralty  instructions  to  overseers. 

Inspection. — The  contract  is  to  be  executed  in  every  respect  to  the  satisfaction  of 
the  Controller  of  the  Navy,  who  will,  as  he  may  see  fit,  appoint  officers  to  inspect  the 
work  while  in  progress.  The  boilers  and  superheaters  are  to  be  proved  by  water-pres- 
sure in  the  presence  of  the  inspecting  officer,  and  means  are  to  be  provided  for  ascer- 
taining their  correct  weight  with  fittings  complete  as  supplied  by  the  contractors.  The 
weight  of  the  water  in  the  boilers,  at  a  height  of  nine  inches  above  the  top  of  the  tubes, 
also  to  be  correctly  ascertained.  The  boilers  are  not  to  be  painted  until  they  have  been 
proved  to  the  satisfaction  of  the  inspecting  officer. 

Delivery. — After  the  boilers  and  superheaters  have  been  proved  they  are  to  be  well 
painted  with  red  lead,  and  are  then  to  be  delivered  complete,  with  fittings  and  spare 
gear,  at . 


154 


STEAM  BOILERS. 


CHAP.  VII. 


13.    Material   for   six    Boilers    of   U.    S.    S.    "  Nipsic." 

(Plate  X.) 


November,    1877. 


Letter  of 
reference. 

Number  of 
sheets. 

Dimensions  in  inches. 

Weight  in  Ibs. 

Parts  of  boilers. 

Boiler-iron. 

24 

170^  X     52        X  H 

41,568 

Shell  of  boiler. 

A 

6 

119    X     87        X   i 

7,040 

Back-head. 

B 

6 

1  08    X      73        X  A 

6,500 

Back  tube  sheet. 

C 

6 

119    X      86       X  A 

7,624 

Front  tube-sheet. 

D 

6 

1  10    X     37i     X  A 

2,813 

Lower  part  of  front  head. 

12 

no    X      33!     X  A 

5,417 

Furnaces. 

12 

no    X     31       X  A 

5,012 

* 

12 

1  10   x    28     xA 

4,527 

tt 

12 

120    X       9i     X  H 

2,564 

Transverse  shell  butt-straps. 

E 

6 

!9i  ) 
and  V  X  H 

1,548 

«                            11 

24 

57     X        9f     X   i) 

12 

54    X       9f     X   iV 

3,220 

Longitudinal  shell  butt-straps. 

12 

30    X        91-     X   i) 

F 

6 

no    X     55       X  i 

3,99* 

Bottom  of  back-head. 

6 

100    X     40       X    ^ 

Back-connection. 

6 

106    X     58       X  i 

5,l64 

«            (t 

12 

75    X     27^     X   i 

3,465 

U                       It 

6 

12 

64    X     42        X    §  1 
44    X     36       X    |  f 

3,600 

Butt-plates  for  front-head. 

24 

128    X     34}     X   i 

14,847 

Gussets. 

6 

106    X      16       X   i 

1,425 

" 

6 

94    X      13^     X    } 

i,  066 

" 

12 

96      X        22           X    \ 

3,548 

<( 

G 

12 

36J  X      2o£     X    1 

758 

Furnace-front. 

H 

12 

34    X      19}     X  4 

667 

"          " 

I 

12 

36    X      16       X  A 

274 

Ashpit-doors. 

J 

24 

23}  X      16}     X   } 

57o 

Furnace-doors. 

IO 

86    X     60       X  A 

4,5°° 

Shell  of  steam-  drums,  gussets,  etc. 

a 

8 

37  (diam.)        X  f 

920 

Heads  of  steam-drums. 

Total  

T  7  C    088 

tjj  ty 

SBC.  12. 


DESIGN,  DRAWINGS,  AND  SPECIFICATIONS. 


155 


MATERIAL  FOR  six  BOILERS  OF  U.  S.  S.  "  NIPSIC." — (Continued.) 


Number  of 
pieces. 

Description. 

Dimensions  in  inches. 

Weight  in 

E 

Parts  of  boilers. 

45 

Round  bar-iron 

i\"  diam.  X  80*  long 

1,000 

Stays. 

5° 

a            « 

if"  diam.  X  6of  long 

M53 

M 

38 

u             '< 

if"  diam.  x  80'  long 

i>774 

« 

Flat  bar-iron  .  .  . 

1'  X  2f 

1,000 

Braces. 

«         » 

i"X3' 

1,000 

Furnaces. 

2i'   X    2*' 

825 

Gussets. 

Total  

7.352 

1,440 

Rivets. 

1"  diam.  X  3%'  !°ng 

i?340 

Shell  double  straps. 

2.535 

N 

|*  diam.  X  3!"  !°ng 

2,200 

«          <*           « 

'  J  tJJ 

9,112 
600 

H 
H 

I'  diam.  X  2J*  long 
|'  diam.  X  a¥  long 

7,100 
45° 

Single  straps  and  heads. 
Gussets  and  back-connections. 

262 

« 

|"  diam.  X  2\"  long 

1  80 

Manhole-frames. 

4,125 

« 

1*  diam.  X  2f  "  long 

2,100 

Front-head  strap,  gussets,  and  fur- 

nace-rings. 

2,250 

10,000 

« 
11 

J*  diam.  X  2^'  long 
|"  diam.  X  2\"  long 

i,  080 
4,650 

Gussets  and  furnace-front. 
Furnaces,  back-connections,  back- 

heads,  manholes,  and  gussets. 

3,525 

M 

J"  diam.  X  2"    long 

1,480 

Furnace-front  and   angle-iron   on 

gussets. 

Total  

20,580 

NOTB.— Twenty-five  per  cent,  is  added  to  the  amount  actually  required  of  each  description  of  rivets. 


156 


STEAM  BOILERS. 


CHAP.  VII. 


13.  List  of  Steel  Plates  for  Boiler  of  Steamer  "  Lookout."    (Plate  X.) 


Letter 
of  reference. 

Number  of 
sheets. 

Dimensions  in  inches. 

Tensile   strength 
in  Ibs.  per  sq.  in. 

Parts  of  boiler. 

A 

95  X  67     X  i 

6o,OOO 

Front-head,  upper  section. 

a 

95  X-67     X  A 

7O,OOO 

Back-head,       " 

B 

89  X  31     X   i 

6o,OOO 

Front-head,  lower  section. 

b 

89  X  31     X  T\ 

7O,OOO 

Back  head,       " 

c 

85  X  52     X   i 

6o,OOO 

Back  tube-sheet. 

D 

I 

85  X  71     X  A 

6o,OOO 

Back-  head,  back  connection. 

I 

192  X  20    X  iV 

6o,OOO 

Bottom  and  sides,  back-connect'n. 

2 

265  X  47i  X  A 

70,OOO 

Shell  of  boiler. 

E 

I 

60  X     8    X  42  X  i 

7O,OOO 

Longit'al  outside  strap,  manhole. 

F 

I 

60  X     8    X  25  X  i 

7O,OOQ 

inside      " 

I 

244  X     8    X  T\ 

7O,OOO 

Circular  strap. 

I 

92  X    8    X  TV 

7O,OOO 

Butt-strap,  back-head. 

2 

92  X  45     X  TV 

6o,OOO 

Furnaces,  front  section. 

2 

92  X  41     X  TV 

6o,OOO 

back  section. 

4 

45  X    5     X  TV 

6o,OOO 

straps. 

I 

55  X  25     x  TV 

70,OOO 

Plate  around  manhole,  front-head. 

2 

26  x  24    x  T\ 

70,000 

«                «                   a                        tt 

4 

24  x  30    X  T\ 

7O,OOO 

Gussets  and  stay-plates. 

2 

18  x  26    X  TV 

7O,000 

H                  11                           11 

6 

2?  X  27     X  A 

70,000 

«             it                  it 

G 

65  (diam.)  X  T\ 

7O,000 

Head  of  steam-drum. 

g 

65  X  5°i  X   i 

6o,000 

Bottom 

75  X  73     X  A 

6o,OOO 

Uptake-  pipe. 

73  X    5    x  A 

6o,OOO 

strap. 

171  X  80    x   1 

7O,OOO 

Shell  of  drum. 

2 

80  X    6£  X  A 

7O,OOO 

Straps  for  drum. 

SEC.  13. 


DESIGN,  DRAWINGS,  AND  SPECIFICATIONS. 


157 


LIST  OF  IRON  PLATES,  RIVETS,  TUBES,  ETC.,  FOR  BOILER  OF  STEAMER  "  LOOKOUT." 


Letter 
of  reference. 

Number. 

Dimensions  in  inches. 

i  sheet. 

9°    X    8    X     | 

H 

2  sheets. 

31   x  i?i  x    4 

I 

2       " 

28    x  16    X     1 

K 

2       " 

2Ii  X  isJ  X     i 

L 

2       " 

32     X  14    X    A 

2       " 

82     X  27     X    A 

2       " 

72     X  24    X     i 

2       " 

54    X  24    X     i 

2       " 

106    X    3     X     i 

2       " 

124    X    Si  X     i 

i  sheet. 

72    X    si  X     i 

2  angle-irons 

96     X     ii  X  ii 

140  stay-bolts. 

i'    diam.  x  8i"  long. 

40         " 

i'       "       X  7i'     " 

30  rivets. 

W  "       X  3i'     " 

170     " 

U'  "        X  3'       " 

280     " 

1  3ff    *<            \/    ,,3*        ** 
15"                  ^    *T 

120       " 

if    "           X    2f  '       " 

5°  ;; 

1  •!                     X    2i" 

53° 

X    2^' 

1  1  60  " 

ir  "    x  2r  « 

500     " 

ii;  ;;    x  *\\  ;; 

600     " 

4                           -^     *"T 

400     " 

r  "  .  x  ?r  " 

1  20  brass  tubes. 

2i*  outside  diameter  by 

6  feet  2$  inches  long. 

No.    12    Birmingham 

gauge. 

CHAPTER  VIII. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 

1.  Laying-off. — The  boiler-plates  having  been  tested  and  examined  as  described 
in  chapter  v.,  they  are  made  to  pass,  first  with  one  side  then  with  the  other  side  up- 
wards, between  two  cylindrical  rollers,  in  order  to  level  and  flatten  them  and  to  smooth 
their  surfaces. 

The  exact  lines  to  which  the  plates  are  to  be  trimmed  and  cut  and  the  flanges  are 
to  be  turned,  and  the  centres  of  all  holes  that  are  to  be  punched  or  drilled  before  the 
flanges  are  turned,  are  now  laid-off  on  the  plates  and  plainly  marked  by  means  of  a 
centre-punch.  The  lines  of  curved  surfaces  are  developed  and  laid  down  in  full  size  on 
paper  or  on  a  board  ;  in  case  several  boilers  are  to  be  constructed  from  the  same  draw- 
ing it  is  well  to  make  wooden  or  sheet-iron  templates  of  irregularly-shaped  plates,  and 

Fig.  15. 


I     o     o 

JX" 


3          > — ^  ( 

°/  \° 


/  \  .x-^ "-^       \  /  " /  ' 

^.(   E/C— >^-r'^->/\i   ;y 

VSn^/  /V  ?^     \     /     /V     /\    Vco^/ 


v 


V 


to  mark  the  positions  of  holes  and  points  which  lie  in  the  same  straight  lines  on  sepa- 
rate sticks,  and  to  transfer  them  thence  to  the  plates  ;  the  rivet-holes  of  seams  are  laid- 

158 


SEC.  1. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


159 


off  by  means  of  thin  board  templates  having  holes  of  the  proper  diameter,  spaced  as  re- 
quired. An  intelligent  and  careful  boiler-maker  will  lay-off  in  this  manner  the  position 
of  all  lines  and  holes,  except  on  flanges  that  are  to  be  turned  ;  frequently,  however,  the 
holes  for  stay-bolts  are  first  laid-off  and  drilled  only  on  one  plate,  and  the  correspond- 
ing holes  in  the  opposite  plate  are  marked  off  from  these  holes  when  the  plates  are 
fitted  in  position.  Instead  of  using  the  centre-punch,  the  position  of  holes  that  are  to 
be  punched  is  often  marked  on  the  plate  by  means  of  a  small  round  stick,  called  the 
marker,  which,  being  dipped  into  some  liquid  whiting  and  passed  through  the  holes  of 
the  template,  leaves  white  circles  on  the  plate. 

Figure  15  represents  the  front-head  and  tube-sheet  of  the  boilers  of  U.  S.  S.  Nipsic 
(see  Plate  XII.),  with  the  rivet-holes  and  centres  of  tube-holes  punched,  manholes  and 
furnace-openings  marked  for  cutting  out,  and  the  flanges  for  securing  the  shell  and  the 
furnace-tubes  marked  for  turning. 

In  bending  plates  to  the  circular  form  the  inner  side  is  slightly  compressed  and  the 
outer  side  is  elongated,  the  neutral  axis  passing  through  the  centre  of  the  plate.  There- 
fore the  length  of  the  plates  for  the  shell  of  a  cylindrical  boiler  with  butt-joints  must 
be  equal  to  the  outside  diameter  of  the  shell  minus  the  thickness  of  the  plate,  multi- 
plied by  3.1416,  or  (d  —  t)  n. 

When  a  cylindrical  shell  or  flue  is  formed  of  alternate  inner  and  outer  rings  with 
overlapping  joints  (see  figure  16),  the  circumferential  length  of  the  plates  forming  the 

inner  rings  is  found  by  multiplying  double  the 
thickness  of  the  plates  by  3.1416  and  subtract- 
ing the  product  from  the  length  of  the  outer 
rings.  In  laying-off  the  rivet-holes  in  the  cir- 
cumferential seams  of  these  plates  space  the 
holes  on  the  outer  plates  as  required  ;  the  dis- 
Flg' 16>  tance  between  the  end  holes  of  each  seam  of 

the  inner  plates  must  be  equal  to  the  distance  between  the  corresponding  holes  of  the 
outer  plates,  less  the  product  of  double  the  thickness  of  the  plates  multiplied  by  3.1416  ; 
mark  the  end  holes  on  the  inner  plates  accordingly,  and  divide  the  distance  between 
them  equally,  according  to  the  number  of  rivets  required  for  the  seam. 

When  the  longitudinal  seams  of  such  cylinders  are  made  with  lap-joints  the  forego- 
ing rales  do  not  give  the  whole  length  of  the  plates,  but  the  distance  between  the  centre 
lines  of  the  rivet-holes  of  the  longitudinal  seam,  and  a  proper  amount  has  to  be  added 
to  the  length  of  the  plate  as  an  allowance  for  lap. 

Figure  17  represents  the  method  of  finding  the  form  of  plates  for  conical  tubes. 


160 


STEAM  BOILERS. 


CHAP.  VIII. 


Draw  an  elevation  of  the  cone,  abed;  continue  the  side  lines  till  they  meet  the  cen- 
tre line  in  o  ;  from  o  as  a  centre  draw 
with  radii  o  c  and  o  a  two  circles, 
and  make  the  arcs  e  Ji  and  f  g  re- 
spectively equal  to  the  required  cir- 
cumferential lengths  of  the  two  ends 
of  the  tube ;  draw  the  radial  lines 
ef  and  g  Ji.  The  figure  efgh  rep- 
resents the  form  of  the  plate  re- 
quired when  the  tube  is  to  be  butt- 
jointed.  In  case  the  tube  is  to  be 
lap-jointed  add  the  amount  neces- 


Fig.  17. 


sary  for  lap  at  each  end  of  the  plate,  as  indicated  by  the  dotted  lines,  i  Jc  and  I  m, 
drawn  parallel  to  ef  and  g  h  respectively. 

When  a  cylindrical  shell  or  flue  is  formed  of  rings  lapping  telescopically,  as  in 
figure  18,  each  ring  is  slightly  conical ;  the  taper  is,  however,  so  small  that  the  method 


Fig.  18. 


Fig!  19. 


of  finding  the  shape  of  the  plate  which  was  illustrated  in  figure  17  cannot  be  used  prac- 
tically, because  the  radius  o  c  would  be  too  long.  The  following  convenient  and  suffi- 
ciently accurate  method  of  finding  the  shape  of  such  plates  is  given  by  Sexton  (see 
figure  19) : 

Draw  a  centre  line  and  mark  on  it  the  width  of  the  plate,  g  h  ;  draw  perpendicular 
lines  through  the  points  g  and  h  ;  find  the  circumferential  lengths  of  the  two  sides  of 
the  plate  by  the  rule  given  above ;  and  from  7i  and  g  respectively  lay  off  one-half  of 
these  lengths  on  the  perpendiculars  on  each  side  of  the  centre  line,  marking  the  points 
thus  found  a,  b,  c,  d,  and  draw  lines  a  c  and  b  d ;  erect  a  perpendicular,  a  e,  to  line  a  c 

in  a,  cutting  the  centre  line  in//  hi  =  *     is  very  nearly  the  versed  sine  of  the  arc 

& 

forming  the  upper  edge  of  the  plate ;  draw  a  curve  by  means  of  a  flexible  batten 


SEC.  1. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


161 


through  the  points  a,  i,  b,  and  a  similar  one  through  c,  d;  then  aibdk  c  will  be  the 
form  of  the  plate.  The  number  of  plates  in  the  circumference  of  the  tube  does  not 
affect  this  rule  ;  the  camber  is  constructed  the  same  way,  whether  for  one  or  for  several 
plates. 

When  a  wedge-shaped  portion,  or  ungula,  is  cut  off  from  a  cylindrical  shell,  as  in  the 
boilers  of  U.  S.  S.  Nipsic  (see  Plate  XII.),  the  plates  forming  the  cylindrical  shell  have 


Fig.  21. 


Fig.  22. 

U 


1  _a  6  c  d 


_6a  1 


to  be  cut  to  a  line  1, — 9,  shown  in  figure  21.  The  method  of  laying-off  this  line  is  illus- 
trated in  figures  20  and  21.  Mark  any  convenient  number  of  divisions  on  the  arc  repre- 
senting the  portion  of  the  shell  cut  away  ;  project  the  points  of  these  divisions  on  the 
side  elevation  of  the  shell,  and  draw  the  parallel  horizontal 
lines  1 — !„  2 — 2,,  3 — 3,,  etc.,  through  these  divisions.  Lay 
off  the  position  of  these  divisions  on  the  developed  plate 
by  measuring  their  distance  on  the  arc  from  9  and  laying 
them  off  from  the  corresponding  point  9  on  the  plate 
(figure  21),  and  erect  perpendiculars  at  these  points  of  divi- 
sion ;  measure  the  length  of  the  lines  1 — 1,,  2 — 2,,  etc.,  in 
the  side  elevation  (figure  20),  and  lay  them  off  on  the  perpendiculars  erected  in  the  cor- 
responding points  of  figure  21.  With  a  flexible  batten  draw  a  fair  curve  through  the 
points  thus  found,  which  will  be  the  required  line. 

To  find  the  shape  of  the  plate  forming  the  slanting  part  of  the  back-head  project  the 
divisions  2,  3,  4,  etc.,  of  the  arc  in  figure  20  on  the  horizontal  line  1—h,  and  mark  the 
points  thus  found  a,  b,  c,  etc.  Lay  off  the  distances  h—i,  h—a,  Ji — 5,  etc.,  both  ways 
from  a  centre  line  on  a  horizontal  in  figure  22,  and  mark  the  points  thus  found  1,  a,  b,  c, 
etc. ;  draw  perpendiculars  through  these  points,  making  Ji — 9,  g — 8,  f— 7,  e — 6,  d — 5, 
c — 4,  6—3,  a — 2,  in  figure  22,  respectively  equal. in  length  to  the  slant  lines  1,— 9,,  1, — 8,, 


162 


STEAM  BOILERS. 


CHAP.  VIII. 


li_7])  ij_ 6,,  1,— 5,,  1, — 4,,  1,— 3,,  1,— 2,  in  the  side  elevation  of  figure  20.  With  a 
flexible  batten  draw  a  fair  line  through  the  points  1,  2,  3,  4,  5,  6,  7,  8,  9,  8,  7,  6,  5,  4,  3, 
2,  1,  in  figure  22  ;  then  draw,  at  a  distance  depending  on  the  width  of  the  lap,  the  line 
x  y  parallel  to  1 — 1,  and  the  curve  x  z  y  equidistant  from  the  curve  1 — 9 — 1. 


Figures  23  and  24  represent  the  method  of  laying-off  a  plate  for  the  cylindrical  shell 
of  a  steam-drum  which  is  to  be  placed  on  the  top  of  a  cylindrical  boiler.  Figure  23 
shows  an  elevation  of  the  steam-drum  and  a  portion  of  the  boiler.  Divide  one-quarter 
of  the  circumference  of  the  drum  into  a  convenient  number  of  equal  parts,  and  from 
these  divisions  draw  lines  parallel  with  the  sides  of  the  steam-drum  and  touching  the 
top  of  the  boiler,  as  in  figure  23.  Find  the  length  of  the  plate  required  by  the  rule 
given  above  for  the  development  of  cylindrical  shells,  and  divide  this  length,  exclusive 
of  lap,  into  four  equal  parts  (see  figure  24),  and  each  of  these  parts  into  the  same  num- 
ber of  parts  as  the  quadrant  in  figure  23,  numbering  the  corresponding  points  alike  to 
avoid  confusion.  Along  the  plate  (figure  24)  draw  a  line,  C  C,  representing  the  distance 
from  the  top  of  the  boiler  in  the  centre  to  the  top  of  the  steam-drum,  and  correspond- 
ing with  the  line  C  D  in  figure  23.  Now  mark  on  each  subdivision  the  distance,  corre- 
sponding to  its  number,  from  the  line  C  D  to  the  top  of  the  boiler,  as  shown  in  figure 
24,  and  through  these  points,  by  hand  or  by  means  of  a  flexible  batten,  draw  a  fair 
curve ;  parallel  to  this  curve  draw  another  at  a  distance  corresponding  to  the  width 
required  for  the  flange. 

When  the  diameter  of  the  steam-drum  does  not  exceed  one-half  of  the  diameter  of 
the  boiler  the  following  shorter  method  is  sufficiently  accurate :  Divide  the  plate  into 
four  equal  parts  and  draw  a  line  corresponding  to  the  top  of  the  boiler,  as  in  the  pre- 
vious case ;  from  this  line  draw  one  short  line  in  the  centre  of  each  of  the  four  divisions, 
corresponding  to  the  points  4,  4,  4,  4  in  figure  24.  Call  the  centre  of  the  plate  and  the 
two  ends  0,  and  the  remaining  two  lines.8  ;  mark  on  the  lines  8  the  distance  fro,m  the 


Ssc.  2.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  163 

level  of  the  top  of  the  boiler  to  the  bottom  of  the  side  of  the  steam-drum,  and  on  the 
lines  4  half  that  distance.  Extend  the  trammel  to  such  a  radius  that,  by  taking  a  con- 
tinuation of  the  lines  8  as  a  centre,  it  will  touch  the  marks  on  lines  8  and  4  ;  and  with 
the  same  radius  describe  arcs  passing  through  the  marks  on  lines  4  and  the  points  0  on 
the  line  C  C. 

Similar  methods  are  employed  in  developing  the  lines  of  intersection  of  other  curved 
surfaces. 

2.  Shearing  and  Planing. — After  the  holes  and  lines  are  laid-off  and  marked  on 
the  plate,  the  next  operations  are  to  punch  or  drill  the  holes  and  to  cut  the  plates  to 
the  exact  shape  and  size  required.     Manholes  and  similar  openings  and  curved  outlines 
are  generally  formed  by  punching  a  series  of  holes,  running  into  each  other,  close  to  the 
line,  the  ragged  edges  being  trimmed  afterwards  with  a  chisel.     When  the  outline  of 
the  plate  is  straight  it  is  either  sheared  or  planed. 

The  shearing-machine  commonly  used  for  this  purpose  has  a  stationary  and  a 
movable  steel  cutter,  the  edges  of  which  form  an  acute  angle  with  each  other,  so  that 
during  the  process  of  shearing  the  action  is  rendered  gradual.  The  motion  of  the  cutter 
is  produced  by  means  of  an  eccentric. 

The  process  of  shearing  recommends  itself  through  its  simplicity,  but  it  distresses 
the  metal  greatly,  especially  in  the  case  of  steel  plates,  and  such  edges  as  have  to  be 
calked  have  to  be  trimmed  afterwards  by  hand  to  the  proper  bevel.  On  this  account 
the  edges  of  plates  should  be  planed  where  careful  work  is  required.  Planing  does  not 
distress  the  metal ;  it  produces  a  smooth  edge,  which  can  be  cut  at  once  to  any  bevel 
required  for  calking.  For  butt-joints  the  edges  must  be  cut  square  and  should  always 
be  planed. 

3.  Bending. — Sheets  are  bent  to  cylindrical  shapes  by  passing  them  through  the 
bending-rollers.     The  primitive  bending-machine  consists  of  two  cast-iron  rolls  laid  side 
by  side,  and  a  third  roll,  which  is  adjustable  vertically,  placed  immediately  over  the 
hollow  between  the  two  lower  rolls  (see  figure  25).     In  hand-power  bending-machines 
set  up  on  this  plan  the  levers  to  turn  the  rolls  are  usually  attached  to  one  end  of  one 
of  the  bottom  rolls  and  to  the  opposite  end  of  the  top  roll. 

In  modern  bending-machines  the  rolls  are  arranged  as  shown  in  figure  26.  Two 
pinching-rolls  are  placed  one  directly  over  the  other  and  geared  together.  The 
upper  roll  is  adjusted  to  the  thickness  of  the  plate  to  be  bent  by  two  strong  set-screws, 
and  may  be  lifted  out  of  the  frame  for  the  purpose  of  removing  the  bent  plate.  The 
third  or  bending  roll  is  placed  to  one  side  of  the  lower  roll,  and  may  be  moved,  by 
means  of  a  double  hand-crank,  bevel- wheels,  and  set-screws,  past  the  lower  roll  toward 


164 


STEAM  BOILERS. 


CHAP.  VIII. 


the  upper  one  ;  this  roll  revolves  by  the  friction  of  the  plate  against  it.     When  this  roll 
is  down  far  enough  to  have  its  top  level  with  the  top  of  the  lower  pinching-roll  a 


Fig.  26. 


\ 


\ 


\ 


Fig.  26. 


plate  passing  between  the  pinching-rolls  will  be  flattened  and  levelled ;  but  when  the 
bending-roll  is  raised  towards  the  upper  roll  the  plate  is  bent  to  a  circle,  since  each 
portion  receives  an  equal  curvature.  By  raising  one  end  of  the  bending-roll  higher 
than  the  other  different  degrees  of  curvature  may  be  given  to  the  two  ends  of  the  plate. 
Sometimes  two  bending-rolls  are  used,  one  on  each  side  of  the  pinching-rolls ;  by  this 
arrangement  the  plates  can  be  bent  nearer  to  the  edge  of  the  sheet  than  can  be  done 
with  three  rolls.  A  template  is  applied  to  the  sheet  from  time  to  time  during  the  pro- 
cess of  bending,  which  is  a  gradual  one,  to  see  whether  the  proper  curvature  has  been 
produced.  The  diameter  of  the  rolls  varies  from  eight  to  twelve  inches. 

4.  Flanging. — When  a  plate  is  to  be  bent  in  a  straight  line  to  an  obtuse  angle  it 
may  be  done  cold  by  means  of  a  set  and  a  sledge-hammer.  This  process,  however,  as  a 
rule,  is  objectionable,  and  should  be  avoided  except  in  extreme  cases.  To  produce 
other  shapes  cast-iron  moulds  of  the  required  form  are  used.  The  outline  of  the  bent 
portion  is  marked  on  the  plate  with  centre-punch  marks ;  the  iron  is  then  heated  to 
redness,  laid  on  the  mould,  and  bent  to  shape  by  hammering.  This  process  of  bending 
the  edge  of  a  plate  at  an  angle  with  the  plate  is  called  flanging.  In  flanging  steel  plates 
it  is  recommended  to  bend  them  as  nearly  as  possible  evenly  along  the  whole  length,  as 
much  as  can  be  done  in  each  heat.  When  a  short  circular  bend  is  wanted  in  the  middle 
of  a  long  piece  it  is  conveniently  and  accurately  done  by  heating  the  piece  in  the  middle 
and  bending  it  over  a  ridge,  the  ends  serving  as  levers. 

Sexton   gives  the  following   practical  instructions  regarding  flanging:    "A  plate 


SEC.  5.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  165 

during  the  process  of  flanging  will  gain  twice  its  thickness  in  length  in  each  flange. 
Thus,  suppose  you  want  to  flange  a  circular  plate  to  have  a  3-inch  flange  all  round, 
and  to  be  3  feet  diameter  after  being  flanged  and  f  inch  thick,  yon  must  not  add  twice 
the  width  of  the  flange  to  the  diameter,  making  3  feet  6  inches,  but  twice  the  width  of 
the  flange,  less  four  times  the  thickness,  making  3  feet  4|  inches.  In  marking  the  plate 
line  out  the  exact  diameter  you  want  it  to  be  after  being  flanged,  then  allow  the  width 
of  the  flange,  less  twice  the  thickness  ;  and,  when  flanged,  the  centre  marks  should  be 
on  the  flange  just  where  the  curve  joins  the  flat.  The  proper  radius  of  the  bend  or  root 
of  a  flange  is  twice  and  one-eighth  the  thickness  of  the  plate  for  the  outside  curve.  In 
heating  the  plate  to  be  flanged,  especially  if  it  is  a  difficult  one,  confine  your  heat  to  as 
little  as  possible  over  the  width  of  the  flange,  but  take  as  long  a  heat  as  you  can.  To 
do  this  as  it  should  be  done  make  your  fire  the  shape  of  the  plate  to  be  flanged.  This 
is  easily  accomplished  by  bending  a  piece  of  thin  iron  and  packing  the  coal  (well  wetted 
and  mixed  like  mortar)  up  to  it  on  the  forge,  or  by  adjusting  a  few  fire-bricks  to  the 
required  shape.  Keep  the  centre  of  your  fire  always  clean;  do  not  allow  dust  or 
clinker  to  accumulate  there,  but  let  it  consist  of  clean  coke,  broken  small,  and  the 
harder  the  better.  If  possible,  have  a  block  or  an  anvil  to  fit  the  flange,  and  do  not,  on 
any  account,  flange  on  a  block  with  sharp  edges." 

A  flange  turned  at  the  circumference  of  a  circular  plate  will  be  slightly  thicker  than 
the  plate  ;  but  in  forming  flanges  in  the  middle  of  a  plate,  like  those  for  attaching  the 
furnace-tubes  of  cylindrical  boilers  to  the  front-head  and  to  the  back  tube-sheet,  the 
metal  has  to  be  spread,  and  at  the  edges  the  flanges  are  much  thinner  than  the  plate. 
Such  flanging  tests  the  ductility  of  the  iron  severely.  When  the  front-heads  of  cylin- 
drical boilers  are  too  large  to  be  made  of  one  plate  it  is  well  to  let  the  seam  run  through 
the  furnaces,  as  it  is  easier  to  form  these  partial  circular  flanges  in  the  two  plates  than 
to  turn  a  complete  circular  flange  in  one  plate.  In  such  a  case  an  extra  allowance  of 
metal  must  be  left  at  the  corners  of  the  flanges,  or  they  must  be  spread  out,  as  shown  in 
figure  15,  before  the  flanges  are  turned  ;  because  the  metal  will  be  drawn  away  from  the 
edges  in  the  process  of  flanging,  and  the  flanges  of  the  two  plates  would  not  meet  in 
their  whole  width  otherwise. 

5.  Punching. — The  rivet-holes  are  either  punched  or  drilled.  During  the  former 
operation  the  plate  rests  on  the  table  of  the  punching-machine,  or  it  is  slung  in  a  chain 
and  suspended  from  a  crane,  being  held  in  position  by  several  men,  who  shift  it.  after 
each  hole  is  formed,  so  as  to  bring  the  stations  of  the  successive  holes  under  the  punch. 
Slight  deviations  from  the  correct  positions  of  the  holes  are  almost  unavoidable  with 
this  process,  and.  in  order  to  avoid  this  source  of  error  and  secure  greater  rapidity  in  the 


166 


STEAM  BOILERS. 


CHAP.  VIII. 


execution  of  the  work,  some  machines  are  arranged  to  punch  several  holes  at  the  same 
time,  and  are  provided  with  a  travelling-table,  which  moves  after  each  stroke  of  the 
punches  automatically  through  the  proper  distance.  Devices  for  spacing  the  holes  me- 
chanically are  of  special  value  for  cylindrical  boiler- work,  since  the  holes  are  punched 
before  the  sheets  are  bent  by  the  rollers,  and  it  is  necessary  to  make  an  accurate  allow- 
ance for  the  difference  of  circumference  of  the  inner  and  outer  sheets. 

Punches  are  made  of  steel,  and  are  generally  cylindrical  with  a  flat  end  (see  figure 


Fig.  28. 


Fig.  27. 


Fig.  29. 


Fig.  30. 


27).  When  a  centre-punch  is  used  to  mark  the  stations  of  the  holes  a  point  is  formed 
at  the  centre  of  the  end  of  the  punch,  as  shown  in  figure  28,  in  order  to  feel  for  the 
puncture.  Reed  says  that  punches  distress  the  iron  less  when  the  ends  are  formed  as 
shown  in  figure  29,  instead  of  being  flat.  Others  claim  an  equal  advantage  for  punches 
with  a  slightly  concave  face,  especially  for  punching  large  holes. 

Figure  30  represents  Kennedy's  helical  punch.  "Its  form  may  be  explained  by 
imagining  the  upper  cutter  of  a  shearing-machine  being  rolled  upon  itself  so  as  to  form 
a  cylinder  of  which  its  long  edge  is  the  axis.  The  die  being  quite  flat,  it  follows  that 
the  shearing  action  proceeds  from  the  centre  to  the  circumference,  just  as  in  a  shearing- 
machine  it  travels  from  the  deeper  to  the  shallower  end  of  the  upper  cutter."  Re- 
sults of  experiments  made  at  Crewe,  England,  on  the  tensile  strength  of  samples  of  the 
same  plate  punched  with  Kennedy's  spiral  and  ordinary  punches  respectively,  showed 
an  average  of  nine  per  cent,  in  favor  of  the  former.  Plates  punched  with  both  punches 
broke  in  every  case  through  the  hole  of  the  ordinary  punch. 

It  is  usual  to  have  the  holes  ^  inch  larger  than  the  rivets,  for  f -inch  rivets,  in  order 
to  allow  for  their  expansion  when  hot ;  it  is  evident,  however,  that  the  difference  be- 
tween the  diameters  of  the  hole  and  of  the  rivet  should  vary  with  the  size  of  the  rivet. 

The  hole  in  the  die  is  made  larger  than  the  punch  ;  for  ordinary  work  the  propor- 
tion of  their  respective  diameters  varies  from  1  :  1.15  to  1  :  1.2.  William  Sellers  &  Co., 


SBC.  5.  LAYING-OFP,  FLANGING,  RIVETING,  WELDING,  ETC.  167 

Philadelphia,  use  the  following  rule  for  proportioning  the  size  of  the  die-hole :  The 
diameter  of  the  die-hole  is  equal  to  the  diameter  of  the  punch  plus  two- tenths  the  thick- 
ness of  the  plate  (D  =  d  -\-  0.2  f).  By  making  the  die-hole  larger  than  the  punch  a 
taper  hole  is  produced  in  the  plate,  and  the  punching  can  be  done  with  less  expenditure 
of  power  and  with  less  strain  on  the  plate. 

Daniel  Adamson  states  that  "the  power  required  to  punch  a  hole  through  a  steel 
plate  equal  to  a  sectional  inch  of  detruding  area  may  be  found  by  multiplying  the 
maximum  tensile  strength  per  square  inch  by  0.74  of  the  same  metal — the  detruding 
area  meaning  the  circumference  of  the  punch  multiplied  by  the  thickness  of  the  plate. 
This  law  may  be  depended  upon  both  for  soft  and  hard  steels." 

The  sheets  must  always  be  punched  from  the  "faying"  surfaces — i.e.,  the  surfaces 
in  contact ;  thus  no  burr  or  roughness  is  left  around  the  holes  to  keep  the  sheets  apart 
or  necessitating  time  and  labor  for  its  removal ;  the  holes  are  also  better  filled  by  ham- 
mering down  the  hot  rivet,  which  assumes  the  form  of  two  frusta  of  a  cone  joined  at 
the  small  ends,  and  brings  the  sheets  in  closer  contact  by  contraction  in  cooling  (see 
figure  31). 

Special  attention  has  to  be  paid  to  this  point  in  punching  the  rivet-holes  in  sheets 
Fig.  31.  that  are  intended  for  cylindrical  shells  and  tubes, 

since  the  holes  at  the  ends  have  to  be  punched 
from  different  sides,  according  to  the  style  of 
joint  used. 

Numerous  experiments  have  established  the 
fact  that  the  strength  of  plates  is  materially  im- 
paired by  punching.  A.  C.  Kirk,  in  a  paper  read 
before  the  Institution  of  Naval  Architects  in  1877, 
says:  "The  effect  of  the  punch  is  clearly  shown  in  the  fracture  by  a  portion  highly 
crystalline  on  each  side  of  the  hole.  This  crystalline  fracture  around  the  hole  is  due  to 
the  bursting  pressure  exerted  by  the  piece  punched  out,  as  it  tends  to  spread  out  in 
diameter  under  the  intense  pressure  of  the  punch.  Under  this  strain  the  metal  is  com- 
pressed for  a  certain  distance  round  the  hole,  and  thus  weakened."  This  zone  of 
injured  metal  does  not  extend  farther  than  £  inch  from  the  hole,  and  the  injurious 
effect  of  punching  may  be  entirely  removed  by  punching  the  holes  somewhat  smaller 
than  the  size  required  and  reaming  or  drilling  them  out  afterwards.  Annealing  after 
punching  restores,  likewise,  to  the  strained  metal  its  former  strength  and  elasticity.  In 
many  establishments  steel  boiler-plates  are  always  annealed  after  punching.  The  inju- 
rious effect  is  diminished  by  increasing  the  proportion  of  the  diameter  of  the  die-hole 


168  STEAM  BOILERS.  CHAP.  VIII. 

to  that  of  the  punch  ;  and  it  is  much  greater  for  steel,  especially  the  harder  qualities, 
than  for  iron. 

The  results  arrived  at  by  different  experimenters  vary  greatly  as  to  the  amount  of 
injury  produced  by  punching,  owing,  no  doubt,  to  differences  of  condition  in  the  process 
and  in  the  quality  of  the  material.  C.  H.  Haswell  concludes  from  recent  experiments 
that  the  resistance  of  riveted  steel  plates  with  the  holes  drilled  is,  according  to  the  tem- 
per of  the  metal,  from  18  to  25  per  cent,  greater  than  when  they  are  punched.  A.  C. 
Kirk  states  that  when  the  diameter  of  the  holes  is  three  times  the  thickness  of  the  plate, 
or  greater,  the  injurious  effect  of  punching  is  inappreciable. 

6.  Drilling. — The  practice  of  drilling  the  holes  instead  of  punching  them  comes 
more  and  more  into  favor,  because  the  metal  is  not  injured  by  this  process  and  the  holes 
are  more  readily  correctly  spaced.  It  is  necessary  to  remove  the  sharp  edge  or  burr  of 
the  drilled  hole  carefully  by  slightly  countersinking  it ;  and  when  the  holes  have  been 
drilled  through  two  or  more  plates  together  the  latter  must  always  be  taken  apart  for 
the  purpose  of  removing  the  burr. 

Fairbairn  considered  the  exactly  cylindrical,  parallel,  and  smooth  drilled  holes  not 
well  adapted  to  rivets.  Besides,  punching  saves  about  one-fourth  the  time  and  labor  as 
compared  with  drilling  as  ordinarily  practised. 

Special  machinery  has  been  introduced  of  late  for  drilling  the  holes  in  the  various 
parts  of  boilers.  In  Harvey 's  Boiler-drilling  Machine  the  cylindrical  shell  of  a  boiler 
is  placed  vertically  upon  a  central  circular  turn-table.  The  machine  is  provided  with 
three  drilling  head-stocks,  which  travel  on  an  outer  rail  around  the  boiler,  and  each  one 
of  which  can  drill  one-sixth  of  the  circumference  of  the  boiler  without  moving  the 
latter.  Each  head-stock  is  provided  with  a  vertical  traverse  for  drilling  the  longitudinal 
seams. 

A  very  convenient  arrangement  for  drilling  the  holes  of  boilers  was  designed  by 
Chief-Engineer  H.  Newell,  U.S.N.,  who  describes  the  method  pursued  in  building  a 
set  of  cylindrical  boilers,  8  feet  in  diameter,  for  the  U.  S.  S.  Galena,  at  the  Navy- Yard, 
Norfolk,  Va.,  in  a  report  transmitted  to  the  U.  S.  Navy  Department,  in  the  following 
words : 

"Figure  2  [Plate  XIV.]  represents  the  method  of  drilling  the  circumferential  butt- 
straps,  which  join  the  two  sections  of  the  boiler-shell.  A  is  a  shaft  of  wrought-iron,  on 
which  slides  and  revolves  easily  the  arm  B,  on  one  end  of  which  is  attached  a  Laubach 
Patent  Portable  Drill,  C,  the  weight  of  which  is  counterbalanced  at  the  other  end  by 
the  weight  E,  made  in  halves,  secured  to  the  arm  by  a  bolt  and  nut.  The  shaft  is  ad- 
justed and  maintained  central  to  the  shell  by  the  tripod  D,  D,  D,  clamped  tightly  to  the 


SEC.  6.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  169 

shaft  by  three  bolts  near  the  centre,  and  to  the  shell  by  set-screws,  as  shown.  The 
back  end  of  the  shaft  is  supported  by  a  block  of  wood  bolted  to  the  back-head  through 
the  holes  intended  for  socket-bolts.  The  power  is  communicated  to  the  drill  from  any 
convenient  distance  and  at  any  angle,  through  a  telescopic  shaft  and  universal  couplings, 
from  a  counter-shaft  (furnished  with  the  patent  drill)  driven  from  the  fly-wheel  of  a 
small  Sewell  steam-pump,  which  is  secured  on  blocks  and  can  be  transported  to  any 
part  of  the  boiler-shop,  steam  being  led  to  it  through  a  rubber  hose  and  the  exhaust 
steam  carried  away  through  another  hose. 

"  The  arm  B  is  moved  from  hole  to  hole  radially  and  fore  and  aft,  and  secured  in 
position  each  time  by  a  set-screw  and  gib  in  the  boss.  With  this  machine  the  entire 
circumference  is  drilled  without  once  moving  the  boiler,  and  as  many  as  360  holes  f£" 
diameter  have  been  drilled  by  it,  through  iron  ^"  thick,  in  one  working  day  of  ten 
hours.  The  drills  are  driven  at  about  250  revolutions  per  minute.  This  speed  is  ren- 
dered possible  by,  and  the  great  efficiency  of  the  machine  is  dependent  on,  the  use  of  a 
fine  stream  of  soapy  water  directed  with  considerable  f  orce  against  the  point  of  the  drill, 
which  is  kept  cool  by  the  rapid  evaporation  of  the  spray  directed  upon  it.  The  water  is 
supplied  from  a  barrel  placed  about  30  or  40  feet  above  the  work,  and  conducted  to  the 
drill  by  a  rubber  hose  with  a  fine  nozzle  at  the  end.  This  height  gives  a  sufficient  head 
to  cause  the  fine  stream  of  water  to  strike  the  point  of  the  drill  with  considerable  force 
and  to  reach  it  in  a  hole  of  any  depth,  and  it  is  immaterial  whether  the  drilling  is  in  an 
upward  or  downward  direction.  With  the  use  of  oil  it  would  be  necessary  to  move  the 
boiler-shell  around  so  as  to  bring  the  drill  always  in  a  downward  direction. 

"  Figure  1  shows  the  arrangement  for  drilling  the  furnace  from  the  inside,  and  also 
the  arrangement  for  drilling  the  flanges  of  the  boiler-heads  from  the  outside.  In  the 
former  the  shaft  F,  having  a  flange  on  one  end,  is  supported  at  each  end  by  a  cast- 
iron  tripod,  H,  H,  H,  adjusted  in  the  furnace  by  means  of  a  set-screw  at  the  end  of  each 
arm.  The  shaft  is  at  liberty  to  revolve  and  to  move  fore  and  aft  in  the  bosses  of  the 
tripods  in  order  to  adjust  the  point  of  the  drill  to  the  holes  in  the  template,  and  is  held 
securely,  while  drilling,  by  a  set-screw  in  the  boss.  The  Laubach  Patent  Drill  is  bolted 
directly  to  the  flange  at  the  end  of  the  shaft  F,  and  is  the  same  as  in  the  last  machine, 
excepting  that  the  limited  space  makes  it  necessary  to  use  a  shorter  feed-screw.  With 
the  outside  drilling-machine  the  same  shaft  A,  tripod  D,  D,  D,  and  centre  part  of  arm 
B  are  used  as  in  figure  2  [Plate  XIV.] ;  one  end  of  the  arm  B  is  lengthened  by  bolting 
to  it  a  bar  of  T-iron,  bent  to  the  form  shown,  in  order  to  bring  the  drill  over  the  edge  of 
the  boiler,  and  also  to  clear  the  projection  of  the  furnace-ends.  The  tripod,  being  in 
three  pieces,  is  passed  through  the  manhole  separately  and  bolted  together  in  place. 


170  STEAM  BOILERS.  CHAP.  VIIL 

The  back  end  of  the  shaft  is  supported  by  a  small  casting,  G,  held  in  position  by  a  bolt 
passed  through  holes  in  the  back-connections  intended  for  securing  the  bracket  to 
which  one  of  the  fore-and-aft  braces  to  the  front-head  is  attached.  For  drilling  the 
flange  of  the  back-head  a  bracket  is  used  to  carry  the  arm  B  in  place  of  the  shaft  A 
used  for  the  front-head.  The  holes  intended  for  socket-bolts  are  utilized  for  securing 
this  bracket. 

"A  template  of  iron  $"  thick  is  used  in  the  furnaces  for  guiding  the  drill  and  to 
avoid  the  loss  of  time  that  would  be  occasioned  by  the  necessity  of  stopping  to  '  draw ' 
the  holes  if  a  template  were  not  used.  This  template  is  laid  out  to  the  proper  pitch  of 
rivets,  and  the  holes  carefully  punched  -fa"  smaller  than  the  finished  size  of  hole.  It  is 
then  put  in  position  and  the  drill  run  through  it  and  the  furnace-sheet,  reaming  the 
holes  out  to  the  proper  size  as  it  goes  through.  After  drilling  one  furnace  the  holes  in 
the  template  are  the  proper  size  for  the  next.  This  device  is  found  to  answer  admi- 
rably, as  the  twist-drills  used  follow  the  punched  holes  and  ream  them  out  equally  on 
all  sides. 

"  To  avoid  the  expense  of  making  templates  for  drilling  the  shells  the  following 
method  is  being  adopted  for  the  two  new  boilers  now  building  here  :  The  outside  longi- 
tudinal straps  and  the  circumferential  edges  of  the  shell-sheets  are  carefully  laid  out 
and  the  rivet-holes  punched  -fa*  smaller  than  the  finished  size  before  bending.  The 
sheets  are  then  bent  and  fitted  together  in  sections,  with  the  outside  and  inside  longitu- 
dinal straps  held  in  place  by  tack-bolts.  Each  section  is  then  put  on  a  rough  turn- 
table mounted  on  a  car-truck  in  the  machine-shop,  and  drilled  by  means  of  a  patent 
drill  capable  of  being  moved  up  and  down  on  an  upright  shaft  erected  for  the  purpose, 
while  each  longitudinal  seam  is  brought  to  the  drill  by  turning  the  shell  round  on  the 
turn-table.  The  punched  holes  in  the  outside  straps  serve  as  templates  to  guide 
the  drill  through  the  shell-sheet  and  inside  strap.  This  machine  averaged  about  240 
holes  in  a  day  of  ten  hours. 

"  The  two  sections  are  then  set  up  on  end,  one  on  top  of  the  other,  and  the  circum- 
ferential butt-strap  carefully  fitted  and  securely  tacked.  The  longitudinal  seams  of  the 
two  sections  are  riveted  up,  the  shell  placed  horizontally  on  rollers,  the  back-head  fitted 
in,  and  the  circumferential  strap  is  then  drilled  by  the  machine  represented  by  figure  2, 
the  f  holes  previously  punched  in  the  edges  of  the  shell-sheets  acting  as  templates  to 
guide  the  drill,  which  reams  them  out  to  their  full  size,  |f ",  an^  then  drills  through  the 
solid  plate.  The  rivet-holes  for  the  heads,  having  been  previously  punched  in  the 
shell-sheet,  are  used  as  templates  for  drilling  the  flanges  of  the  heads,  using  the 
machine  represented  in  figure  1  and  previously  described.  This  machine  has  drilled 


SBC.  7.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  171 

• 
two  rows  of  holes  around  the  entire  head  (from  180  to  200)  in  eight  hours,  including  the 

time  expended  in  moving  the  shell  around  to  get  at  the  holes  at  the  bottom  of  the 
boiler.  After  the  furnaces  have  been  secured  in  place  the  front-head  is  fitted  and 
drilled  in  the  same  manner." 

One  man  and  two  apprentices  are  required  to  run  these  machines.  The  man  attends 
to  the  feed  of  the  drill,  one  apprentice  directs  the  nozzle  of  the  hose,  and  the  other  ap- 
prentice stops  and  starts  the  engine,  which  is  provided  with  a  brake. 

It  is  necessary  'to  be  careful,  especially  in  drilling  deep  holes,  to  let  the  jet  of  the 
lubricant  strike  the  end  of  the  drill  constantly. 

7.  Riveting. — The  holes  having  been  drilled  or  punched,  the  sheets  are  fixed  in 
position  and  temporarily  secured  by  bolts  and  nuts.     When  the  holes  have  not  been 
accurately  spaced,  so  as  to  be  "half -blind,"  or  not  perfectly  coincident  in  the  joint, 
Fig.  32.  it  is  a  common  practice  to  resort  to  " drifting" '  —i.e.,  to  drive 

through  both  a  tapered  steel  pin  or  drift,  thus  drawing  the  sheets 
up  and  enlarging  the  holes  by  main  force.  This  practice  pro- 
duces highly  injurious  strains  on  the  sheets  ;  it  causes  the  edges 
of  the  holes  to  bulge  and  gives  to  the  holes  irregular  shapes,  diffi- 
cult to  fill  with  the  rivet  (see  figure  32).  Sometimes,  when  the  want  of  coincidence  is 
slight,  a  smaller  rivet  is  inserted.  Both  practices  are  to  be  condemned ;  such  imper- 
fect holes  should  be  reamed  or  drilled  out,  and  a  larger  rivet  should  be  used  which  will 
fill  and  cover  the  enlarged  hole  completely. 

The  operation  of  riveting  by  hand  requires  the  services  of  two  "riveters"  and  one 
"helper"  in  the  gang,  besides  the  boy  who  heats  the  rivets  in  a  forge.  The  shank  of 
the  rivet  is  brought  to  a  white  heat,  but  the  head  is  not  made  quite  so  hot ;  care  has  to 
be  taken  not  to  burn  the  rivet.  The  boy  passes  the  rivet  to  the  helper,  who  places  it 
in  the  hole,  drives  the  head  close  up  to  the  plate,  and  holds  a  heavy  hammer  or  other 
mass  of  iron  firmly  against  the  head  of  the  rivet  while  the  riveters  beat  the  protruding 
end  of  the  shank  into  the  required  shape.  First,  however,  they  strike  a  few  blows 
arcmnd  the  rivet-hole  on  the  plate  to  bring  the  sheets  into  close  contact.  The  first  blows 
on  the  rivet  must  fall  squarely  on  the  point,  so  that  the  rivet  is  upset  throughout  its 
whole  length  and  fills  the  hole  completely  before  a  shoulder  is  formed.  According  to 
the  form  to  be  given  to  the  point,  the  rivet  is  either  beaten  down  roughly  to  shape  and 
then  finished  by  a  "  set,"  or  cup-shaped  die,  held  by  one  riveter  and  struck  with  a  heavy 
hammer  by  the  other ;  or  it  is  beaten  to  a  conical  shape  with  light  hammers.  The  ham- 
mers used  by  riveters  vary  from  2  to  7  Ibs.  in  weight,  according  to  the  character  of  the 
work  and  the  size  of  the  rivets  ;  and  the  holding-up  hammers  weigh  from  10  to  40  Ibs. 


172  STEAM  BOILERS.  CHAP.  VIII. 

To  drive  each  f -inch  rivet  an  average  of  250  blows  of  the  hammer  is  needed.  The 
largest  rivets  that  can  be  worked  by  hand  are  1J  inches  in  diameter.  For  the  operation 
of  riveting  expert  and  skilful  workmen  are  required,  that  the  rivets  may  be  fixed  sound 
and  firm  and  that  all  unnecessary  hammering  may  be  avoided.  The  conical  points  of 
the  rivets  become  brittle  and  are  liable  to  crack  or  drop  off  altogether  when  the  ham- 
mering is  continued  after  they  have  grown  cold. 

Daniel  Adamson,  in  a  paper  read  before  the  Iron  and  Steel  Institute  in  1878, 
states  as  his  experience  that  "nearly  all  ordinary  bar  or  boiler  irons  and  mild  steels 
will  endure  considerable  percussive  force  when  cold  and  up  to  450°  Fahr.,  after  which, 
as  the  heat  is  increased,  probably  to  near  700°,  they  are  all  more  or  less  treacherous  and 
liable  to  break  up  suddenly  by  percussive  action." 

The  specimens  experimented  upon  stood  the  bending  test  perfectly  when  cold  and 
at  a  red  heat. 

Modern  direct-acting,  steam  or  hydraulic  riveting-machines  have  a  cup-shaped  die 
on  the  end  of  the  piston-rod,  which  presses  against  a  fixed  die.  The  work  is  brought 
into  position  for  riveting  by  cranes ;  the  rivets  are  placed  in  the  holes  by  hand,  the 
pressure  is  admitted  to  the  cylinder,  and  the  die  on. the  piston-rod  is  pressed  forward 
upon  the  hot  rivet  and  squeezes  it  into  shape. 

The  riveting-machine  accomplishes  this  work  with  great  rapidity  and  regularity, 
without  the  disagreeable  noise  of  hand-riveting ;  the  sheets  are  pressed  close  together 
during  the  operation,  and  the  rivets  are  acted  upon  while  at  the  proper  temperature ; 
the  steady  pressure  compresses  them  evenly  throughout  their  length,  till  the  plastic 
metal  flows  into  every  irregularity  of  the  rivet-hole,  and  the  surplus  metal  may  be 
formed  into  heads  of  any  size  and  form. 

It  is  found  that  rivets  driven  by  hand  fill  up  the  hole  very  well  immediately  under 
the  points  formed  by  the  hammer,  but  that  the  same  effect  is  not  produced  at  every 
point  in  the  length  of  the  rivet,  especially  when  the  holes  are  irregular.  So  great  is  this 
difficulty  that  in  hand-riveting  shorter  rivets  must  be  used,  because  it  is  impossible  to 
work  effectively  so  large  a  mass  with  a  hammer  as  with  a  machine.  The  heads  of  the 
machine-rivets  are,  therefore,  larger  and  stronger,  and  will  hold  the  plates  together 
more  firmly  than  the  smaller  hand-riveted  heads.  There  are,  however,  many  parts  of 
a  boiler  that  are  inaccessible  to  the  machine  and  must  always  be  riveted  by  hand. 

Figure  33  represents  the  steam-riveting  machine  built  by  the  Providence  Steam- 
engine  Company,  Providence,  H.  I.  It  has  an  annular  die,  A,  surrounding  the 
cupped  die  which  acts  on  the  rivet,  both  dies  having  an  independent  horizontal  motion. 
The  middle  lever,  B,  acts  on  the  cupped  die,  and  the  two  levers  C  C  act  on  the  annu- 


SEC.  7. 


LAYENG-OFP,  FLANGING,  RIVETING,  WELDING,  ETC. 


173 


lar  die.  The  long  arm  of  each  lever  is  connected  by  means  of  a  forked  rod  to  the  piston 
of  the  single-acting  steam-cylinders,  D  and  E.  When  the  work  has  been  moved  into 
position  between  the  standard  F,  carrying  a  stationary  cupped  die  which  bears  against 


FIG.33 


the  head  of  the  rivet,  and  the  movable  dies,  the  slotted  sliding-bar  L  is  moved  by 
means  of  the  handle  H.  This  sliding-bar  operates  the  steam-valve  of  each  cylinder, 
regulating  the  admission  and  exhaust  of  the  steam,  and  is  adjusted  in  such  a  manner 
as  to  admit  steam  to  the  cylinder  E  first,  so  that  the  annular  die  strikes  a  blow  around 
the  rivet-hole,  forcing  the  plates  into  close  contact,  and  while  it  is  held  in  that  position 
a  further  motion  of  the  handle  H  admits  steam  to  the  cylinder  D  which  works  the 
cupped  die.  The  latter  is  made  to  deliver  one  or  two  powerful  blows  on  the  point  of 
the  rivet. 

In  TweddeWs  hydraulic  machine-tools  the  power  is  furnished  by  an  hydraulic  ac- 


174  STEAM  BOILERS.  CHAP.  VIII. 

cumulator,  consisting  of  a  cast-iron  cylinder  in  which  a  plunger  moves  which  carries 
the  weight  producing  the  pressure  on  the  water  pumped  into  the  cylinder.  For  punch- 
ing and  shearing  machines  Tweddell  uses  a  water-pressure  equal  to  about  fifty  atmos- 
pheres. 

His  riveting-machines  are  worked  by  special  accumulators  capable  of  exerting  a 
pressure  of  about  100  atmospheres.  They  consist  of  a  vertical  cylinder,  loaded  with 
weights,  which  moves  along  a  plunger  fixed  at  the  lower  end  and  having  a  channel 
through  the  centre  which  establishes  communication  between  the  pumps  and  the  annu- 
lar space  between  the  cylinder  and  the  plunger.  The  volume  of  water  contained  in  the 
accumulator  is  small,  and  consequently  the  fall  of  the  cylinder  during  the  operation 
of'  the  machine  is  relatively  great ;  the  vis  viva  of  the  falling  counter- weights  being  de- 
signed to  increase  the  effect  of  the  water-pressure  as  the  ram  of  the  riveting-machine  is 
arrested. 

The  use  of  hydraulic  power  has  special  advantages  for  riveting-machines :  violent 
shocks  are  avoided,  and  the  pressure  on  the  ram  may  be  varied  at  will  for  different 
kinds  of  work  by  changing  the  weights  on  the  acciimulator.  Each  rivet,  whether  long 
or  short,  is  driven  with  a  single  progressive  movement,  controlled  at  will  by  the  operator. 

These  riveting-machines  are  made  either  stationary  or  portable.  In  stationary 
machines  the  hydraulic  cylinder,  made  of  bronze,  is  firmly  attached,  in  a  horizontal 
position,  on  the  top  of  a  heavy  cast-iron  frame ;  the  die  fixed  to  the  end  of  the  ram 
is  made  of  wrought-iron. 

In  the  portable  riveters  the  hydraulic  ram  acts  on  a  lever,  the  arms  of  which  have 
the  proportions  of  two  to  one  ;  the  die  is  fixed  to  the  short  end  of  the  lever,  the  fulcrum 
being  at  the  long  end,  but  provision  being  sometimes  made  to  interchange  the  position 
of  the  die  and  the  fulcrum.  A  fixed  die  is  attached  in  a  corresponding  position  to  the 
casting  of  the  hydraulic  cylinder.  In  the  different  sizes  of  these  portable  hydraulic  riv- 
eters manufactured  by  Wm.  Sellers  &  Co.,  Philadelphia,  the  levers  are  made  6  inches 
and  12  inches  long,  9  inches  and  18  inches  long,  and  12  inches  and  24  inches  long  respec- 
tively. The  portable  riveter  rests  in  a  frame  having  the  form  of  a  quadrantal  arc,  by 
which  it  is  suspended  from  a  hoisting-machine  on  an  overhead-carriage  travelling  on 
rails.  By  this  means  the  riveting-machine  can  be  placed  in  any  position  required  for 
the  work  to  be  done,  and  moved  over  a  large  area ;  the  work  rests  on  trestles  and  the 
riveting-machine  is  moved  along  or  around  it.  The  water  is  carried  from  the  accumu- 
lator to  the  riveting-machine  through  jointed  or  flexible  pipes. 

The  operation  of  the  machine  is  described  by  the  manufacturers  as  follows : 

"  One  man  raises  and  lowers  the  riveter,  adjusts  it  to  the  rivets,  and  then  closes  the 


SEC.  7. 


LAYING-OFP,  FLANGING,  RIVETING,  WELDING,  ETC. 


175 


dies  on  the  rivets.  Boys  drop  the  red-hot  rivets  into  place,  with  the  head  of  the  rivet 
uppermost  in  horizontal  work.  With  a  skilful  operator  as  many  as  6  to  10  red-hot 
rivets  may  be  put  in  place  ahead  of  him,  and  he  can,  on  beam- work,  drive  from  10  to 
16  rivets  per  minute. 

"In  using  the  hydraulic  riveting-machine  to  advantage  the  rivets  should  be  heated 
rapidly  and  uniformly." 

The  weight  of  a  portable  riveter  capable  of  driving  rivets  £  inch  in  diameter  is  about 
450  Ibs. 

The  number  of  rivets  put  in  for  a  day's  work  depends  upon  the  diameter  of  the 
rivets,  their  position  with  regard  to  greater  or  less  accessibility,  the  description  of  the 
points,  and  the  care  taken  during  the  operation.  Reed  furnishes  the  following  table  as 
representing  the  practice  of  hand-riveting  at  a  large  English  private  shipyard  (a  day's 
work  is  taken  at  ten  hours) : 


Position  of  rivets. 

Diameter  of  rivets  and  description  of  points. 

Number    of  rivets 
put  in  by  a  set  of 
riveters      for     a 
day's  work. 

In  outside  plating  

i  ~mch  countersunk 

3c  to  QO 

In  bulkheads,  etc  

f-inch,  snap  

I  80 

In  made  beams,  etc  

•f-inch,  snap  

2OO 

In  beam  ends  

i~mch  to  4-^-inch  hammered 

CO 

In  deck-plating  

•J-inch    countersunk 

5° 

Fairbairn  states  that,  with  two  men  and  two  boys  attending  to  the  plates  and  rivets, 
his  machine  could  fix  8  rivets  of  f  diameter  per  minute,  while  three  men  and  one  boy, 
by  hand-riveting,  could  only  fix  40  rivets  per  hour ;  hence  the  quantity  of  work  done 
in  the  two  cases  was  as  12  to  1,  and  one  man's  labor  was  saved. 

Grantham  states  that  with  Garforth's  riveting-machine  6  rivets  can  be  put  in  per 
minute,  while  20  rivets  per  hour  is  the  work  of  a  set  of  riveters. 

At  Pittsburgh,  Louisville,  and  other  places  west  of  the  AHeghanies  rivets  are  driven 
cold  in  boiler- work.  It  is  evident  that  none  but  the  very  best  material  can  be  nsed  for 
such  rivets,  and  this  is  claimed  as  an  advantage  for  this  process ;  besides,  these  rivets 
are  free  from  the  danger  of  being  burnt,  and  cannot  become  loose  in  the  hole  by  con- 
tracting diametrically  in  cooling  after  being  hammered  down.  The  extensive  use  of 
cold-hammered  rivets  in  the  high-pressure  boilers  of  the  Western  river-steamers  proves 
conclusively  that  tight  joints  can  be  made  with  cold  rivets.  When  the  total  thickness 


176 


STEAM  BOILERS. 


CHAP.  VIII. 


of  the  plates  is  more  than  4  inches  it  is  better  not  to  employ  hot-riveting,  because  the 
contraction  in  cooling  might  spring  up  or  shear  off  the  head  of  the  rivet ;  instead  of 
using  cold  rivets  of  such  great  length  it  is  often  better  to  use  turned  screw-bolts  of  very 
slight  taper. 

In  using  steel  rivets  care  must  be  taken  to  heat  them  uniformly,  not  above  a  cherry- 
red  heat,  and  to  work  them  down  and  finish  them  off  as  quickly  as  possible.  Reed 
says  on  this  point:  "When  the  [steel]  rivet  has  not  been  sufficiently  heated,  or  the 
riveters  have  not  been  expert,  they  have  had  great  trouble  in  cutting  off  the  burr,  and 
in  doing  so  have  often  broken  away  part  of  the  countersunk  point  with  the  burr.  On 
the  other  hand,  if  the  rivets  are  heated  much  above  a  cherry-red  heat  they  cannot  be 
properly  knocked  down,  as  they  waste  away  under  the  blows  of  the  hammer.  If  great 
care  is  not  taken  the  rivet  may  be  overheated  to  an  extent  not  sufficient  to  prevent  its 
being  knocked  down,  but  sufficient  to  greatly  deteriorate  the  quality  of  the  finished 
rivet.  It  is  advantageous  to  have  plain  knock-down  or  conical  points  to  steel  rivets  in 
preference  to  snap-points,  as  a  burnt  or  overheated  rivet  is  then  more  easily  detected  by 
the  crack  round  the  edges." 

8.  Forms  of  Rivets. — Rivet  heads  and  points  are  of  various  shapes.  Figure  34 
shows  the  dimensions  of  a  f-inch  rivet  of  the  form  most  commonly  used  in  boiler- 
making.  In  hand-riveted  boilers  the  rivet-points  are  generally  made  conical  (figure  35). 


Fig.  34. 


Fig.  35. 


Fig.  36. 


Fig.  37. 


The  riveting-machine  and  the  hand-set  make  hemispherical  heads  and  points,  also 
called  snap-points  (figure  36).  In  places  where  it  is  essential  to  preserve  a  smooth  sur- 
face the  rivets  are  countersunk  (figure  37). 

The  lengths  of  shank  required  to  form  these  different  rivet-points  are  given  in  the 
following  table : 


SBC.  9. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


177 


TABLE  XXV. 


Kind  of  point. 

Length  cf  shank  required. 

Countersunk  point 

for  2  thicknesses  of  sheets  

i  diameter 

*i                                 U 

for  3  thicknesses  of  sheets  

i  diam  -|-  i  inch 

Snap-points  

Snap-points  present  generally  a  greater  area  of  metal  to  resist  shearing  than  conical 
points ;  they  are  also  considered  stronger,  because  in  forming  them  by  means  of  a  die 
the  metal  is  compressed,  while  in  the  hand-hammered  conical  point  the  metal  is  spread. 
Snap-points  cannot  well  be  formed  on  hand-hammered  rivets  over  £  inch  diameter, 
because  too  heavy  a  hammer  would  be  required.  Snap-points  are  extensively  used  for 
interior  work  in  shipbuilding. 

Conical  points  are  considered  to  make  a  tighter  joint,  since  they  cover  a  larger  sur- 
face. The  height  of  the  cone  should  be  about  three-quarters  of  the  diameter  of  the 
rivet ;  if  made  too  flat  they  are  weak  and  waste  away  rapidly  through  corrosion. 

The  enlarged  hole  necessary  for  countersunk  rivets  weakens  the  plate,  while  the 
rivet  is  correspondingly  stronger.  They  are  used  necessarily  for  the  outer  plating  of 
vessels.  In  boiler-making  they  are  only  used  on  the  strengthening-rings  of  manholes 
and  other  openings,  on  furnace-fronts,  and  where  it  is  necessary  to  clear  a  flange,  etc. 
Countersunk  rivets  should  be  avoided  where  the  stress  on  them  consists  in  a  pull  in  the 
direction  of  their  length. 

Sexton  recommends  to  use  a  uniform  angle  of  60°  for  the  countersinking  tool  for 
Fig.  38.  holes  of  all  sizes,  and  not  to  countersink  the  hole  down  to  a  thin 

5  \  /  ~7  edge,  but  to  leave  a  portion  of  it  cylindrical,  say  about  one-fourth 
of  the  thickness  of  the  sheet  (figure  38).  Other  writers  recom- 
mend to  use  such  an  angle  that  the  apex  of  the  cone  falls  on  the  line  where  the  shank 
joins  the  head  of  the  rivet. 

9.  Styles  of  Joint. — Riveted  joints  are  either  lap-joints  or  butt-joints.  In  the 
former  case  the  edges  of  the  plates  lap  one  over  the  other  a  certain  width  called  the  lap, 
and  the  rivets  are  put  through  both  sheets.  In  the  other  case  the  edges  butt  against 
each  other  and  are  covered  by  one  or  two  narrow  strips  of  plate  called  welts  or  butt- 
straps,  which  are  riveted  to  each  plate.  The  rivets  are  placed  either  all  in  one  line  at 


178 


STEAM  BOILERS. 


CHAP.  VIII. 


an  equal  distance  from  the  edge,  or  in  several  rows  ;  and  in  the  latter  case  they  are  put 
either  directly  behind  each  other  (chain-riveting)  or  staggered — i.e.,  in  zigzag  lines. 

The  following  are  the  principal  styles  of  joint  used  in  boiler-making : 

Figure  39  represents  a  single-riveted  lap-joint. 

Figure  40  represents  a  double-riveted  lap-joint. 

Figure  41  represents  a  single-riveted  butt-joint  with  single  butt-strap. 

Figure  42  represents  a  single-riveted  butt-joint  with  double  butt-strap. 

Figure  43  represents  a  double-riveted  butt-joint  with  double  butt-strap. 

Figure  44  represents  a  chain-riveted  butt-joint  with  double  butt-strap. 


Fig.  39. 


Fig.  40. 


Fig.  41. 


Fig.  42. 


Fig.  43. 


Fig.  44. 


In  bridge-building  and  ship-building  a  greater  number  of  rows  of  rivets  are  often 
advantageously  employed.  In  boiler-making  the  objects  to  be  kept  in  view  in  selecting 
a  special  kind  of  joint  and  proportioning  it  are  strength,  economy  of  material  and  labor, 
and  tightness. 

1O.  Friction  in  Riveted  Joints. — E.  Clark  and  Reed  have  made  experiments  to 
determine  the  amount  of  friction  in  riveted  joints  due  to  the  force  exerted  on  the  sheets 


SEC.  10. 


LAYING-OPF,  FLANGING,  RIVETING,  WELDING,  ETC. 


179 


by  the  contraction  of  the  rivets  in  cooling.  Reed  describes  his  experiments  in  the  fol- 
lowing manner :  "  Three  plates  were  united  by  what  is  known  as  a  chain-joint — that  is, 
the  ends  of  the  two  outer  plates  overlapped  the  end  of  the  middle  plate.  The  connec- 
tion of  the  plates  was  made  by  three  rivets  passing  through  the  lap,  the  rivet-holes  in 
the  outer  plates  being  filled  by  the  rivets,  but  the  bearing-surface  of  the  holes  in  the 
middle  plate  being  slotted  out  as  shown  in  figure  45.  It  will  thus  be  Fig.  45. 
obvious  that  when  a  tensile  strain  was  brought  upon  the  middle  plate 
the  amount  of  the  friction  could  be  measured  by  the  force  just  able  to 
produce  a  sliding  motion.  The  breadth  of  the  lap  was  three  diame- 
ters, the  rivets  were  a  diameter  clear  of  the  edge  of  the  plates,  and 
their  pitch  was  four  diameters." 

Both  iron  and  steel  plates  were  experimented  on  with  different 
kinds  of  rivets  ;  the  dimensions  of  the  plates  were  \"  X  8J",  the  rivets 
being  f "  ;  and  £"  x  11",  the  rivets  being  1  inch.  The  mean  weight  re- 
quired to  cause  the  plates  to  slide  was  4.95  tons  per  rivet.  Reed  sums 
up  the  result  of  his  experiments  in  the  following  words:  "It  thus 
appears  that  rivets  with  pan-heads  and  conical  points  have  the  advan- 
tage over  both  the  other  descriptions  of  riveting."  .  .  .  "It  also  becomes  evident 
that  countersunk  riveting  causes  much  less  friction  than  the  other  systems.  On  com- 
parison it  will  be  seen  that  in  nearly  all  cases  steel  plates  and  rivets  give  less  friction 
than  iron."  .  .  .  "The  use  of  larger  rivets  with  the  same  pitch,  etc.,  gives  an  in- 
crease in  the  friction,  but  no  law  of  increase  appears  to  be  conformed  to." 

The  results  of  Clark's  experiments  did  not  differ  much  from  Reed's. 

In  commenting  on  these  results  "Wilson  remarks:  "It  must  not,  however,  be  con- 
cluded that  the  value  of  a  rivet  is  to  be  determined  by  adding  to  its  shearing  strength 
the  amount  of  friction  between  the  plates  produced  by  its  contraction  in  cooling.  Al- 
though these  two  elements  of  strength  act  together  in  a  well-filled  hole,  they  cannot  be 
considered  as  acting  independently."  ..."  The  manner  in  which  a  severe  tensile 
strain  affects  a  lap-joint  by  pulling  it  athwart  the  line  of  strain  (see  figure  46)  must  also 

tend  to  diminish  the  friction  of  the  plates.     Long 
before  the  ultimate  resistance  of   the   joint  is 


Fig.  46. 


1  reached,  especially  with  single-riveting,  the  fric- 
tion of  the  plates  must  be  greatly  diminished, 
and  cannot  be  regarded  as  materially  influencing 
the  ultimate  strength  of  the  joint.  In  old  boilers  it  is  probable  that  the  tension  of  the 
rivet  becomes  gradually  eased  by  the  continual  straining  and  alteration  of  temperature, 


180  STEAM  BOILERS.  CHAP.  VIII. 

which  will  in  time  affect  the  nature  of  the  iron."  ...  "  There  can  be  no  doubt  that 
severe  calking,  as  commonly  practised,  must  tend  to  diminish  the  friction  between  the 
plates,  especially  when  they  are  thin." 

11.  Straining  Action  on  Riveted  Joints. — "A  riveted  joint  is  in  a  certain 
sense  an  imperfect  part  of  a  structure.  It  cannot  be  so  designed  as  to  be  throughout 
uniformly  strained.  It  has  always  certain  surfaces  markedly  weaker  than  the  rest,  at 
which  consequently  deterioration  of  the  material  or  fracture  by  the  action  of  the  load  is 
liable  to  occur.  These  surfaces  of  weakness  are  so  related  that  in  general  the  increase 
of  one  involves  a  diminution  of  the  other.  The  joint,  therefore,  which  will  carry  the 
greatest  load  before  fracture  will  be  that  in  which  the  stress  reaches  the  breaking  limit 
for  each  of  these  surfaces  simultaneously.  Since  the  rivet-section  can  in  general  be  in- 
creased only  at  the  expense  of  the  plate-section,  in  the  strongest  joint  the  rivet  and 
plate  will  reach  their  breaking-point  under  the  same  load.  It  would  seem,  therefore, 
that  the  proportions  of  a  riveted  joint  could  be  determined  by  the  ordinary  rules  of 
applied  mechanics  without  the  need  of  experiment.  That  this  is  not  so  is  probably 
mainly  due  to  a  second  condition  of  imperfection  in  riveted  joints.  To  apply  the 
ordinary  rules  for  the  strength  of  materials  to  riveted  joints  it  is  necessary  that 
the  distribution  of  the  stresses  on  the  surfaces  of  weakness  should  be  known.  If 
those  stresses  were  as  uniformly  distributed  as  in  an  ordinary  bar  tested  for  tension 
or  for  shearing,  the  problem  would  be  simple.  But,  in  fact,  the  stresses  are  less 
uniformly  distributed  and  the  law  of  their  distribution  is  unknown.  Consequently 
the  average  stress  on  the  surface  of  fracture  of  a  riveted  joint,  when  broken  by  a 
load,  is  less  than  it  would  be  if  the  stress  were  uniformly  distributed,  and  needs 
to  be  determined  by  special  experiments.  Further,  it  may  be  different  for  dif- 
ferent forms  of  joint.  This  average  stress,  always  less  than  the  maximum  stress 
which  causes  fracture,  is  here  termed  the  apparent  breaking  stress.  Hence  the 
chief  object  of  experiments  on  riveted  joints  is  to  determine  the  apparent  break- 
ing stresses — 

(1)  for  the  different  surfaces  at  which  each  joint  may  fracture, 

(2)  for  the  different  forms  of  joint. 

"In  certain  cases  allowance  may  have  to  be  made  for  progressive  deterioration  of  a 
joint,  by  corrosion  or  otherwise,  which  reduces  the  strength  in  certain  directions  more 
than  in  others.  No  experiments  showing  the  amount  of  deterioration  in  such  cases 
appear  to  have  been  made. 

"Let  a  bar  be  broken  at  the  plane  ab  of  area  w  (figure  47)  by  a  tension,  T,  acting 
normally  to  the  section. 


SEC.  11. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


181 


"  Then  if  the  stress  is  uniformly  distributed  over  the  section  at  the  moment  of 

T 

fracture  the  ratio  -  -  is  the  real  tenacity  of  the  material.  But  if  it  is  not  uniformly 

w  * 


Fig.  48.    Fig.  48.o  pig.  49.     F'g-  50 

»P  tP  e  a     ic 


T 

distributed  then  --  is  only  the  apparent  tena- 
city, and  this  may  be  less  than  the  real  tena- 
city to  any  extent  whatever.  It  may  be  useful 
to  consider  under  what  conditions  the  distri- 
bution of  stress  necessarily  becomes  unequal. 

"  (1.)  It  will  cease  to  be  uniform  if  the 
resultant  P  of  the  load  does  not  pass  through 

the  centre  of  figure  of  the  section.  Thus,  in  the  case  shown  in  figure  48  the  stress  is  a 
varying  stress,  which,  however,  varies  regularly  so  long  as  the  limit  of  elasticity  is  not 
passed.  Some  of  the  discrepancies  in  the  results  of  experiments  on  riveted  joints  are 
probably  due  to  want  of  care  in  ensuring  the  coincidence  of  the  line  of  action  of  the 
load  with  the  centre  line  of  the  joint,  in  the  plane  parallel  to  the  surface  of  the  plates. 
Figure  48a  shows  how  unequal  distribution  of  stress  may  arise  from  this  cause.  In  the 
plane  at  right  angles  to  this  there  is  probably  always  deviation  of  the  load  from  the 
centre  of  figure.  In  lap-joints  the  load  has  to  be  transmitted  from  one  plate  through 
the  rivet  to  the  other  plate ;  in  butt-joints  from  one  plate  through  the  rivets  to  the 
cover-strip  and  back  to  the  other  plate.  In  both  cases,  and  especially  in  the  former 
case,  the  eccentricity  of  the  load  appears  to  cause  a  reduction  of  strength. 

" (2.)  The  stress  maybe  rendered  unequal  by  the  local  action  of  contiguous  material. 
Thus,  a  bar  with  square  corners  (figure  49)  is  known  to  break  with  a  low  apparent 
tenacity.  The  unstrained  material  at  a  prevents  the  elongation  of  the  contiguous  mate- 
rial at  b,  which  consequently  gets  an  excessive  proportion  of  the  load,  and  the  fracture 
begins  at  the  corners. 

"Now,  in  the  portion  of  metal  between  two  rivet -holes  a  similar  action  probably 
occurs.  The  outside  fibre  a  b  (figure  50)  has  less  freedom  of  elongation  than  the  central 
fibre  c  d,  because  it  is  attached  to  the  comparatively  unstrained  material  behind  the 
rivet.  Hence,  instead  of  breaking  simultaneously  over  the  whole  section,  fracture 
probably  begins  at  the  edges  of  the  hole,  and  proceeds  because  the  reduction  of  area 
causes  increase  of  stress  in  the  part  remaining  unbroken.  This  is  sometimes  shown  by 
the  fact  that  the  parts  of  the  plate  will  not  fit  after  fracture.  There  appears  to  be  a 
slight  reduction  of  strength  in  plates  with  a  hole  drilled  in  them  as  compared  with  solid 
plates,  and  this  is  probably  due  to  the  cause  now  under  consideration.  It  is  also  pro- 
bable that  this  reduction  of  strength  may  really  be  greater  than  appears  in  these 


182 


STEAM  BOILERS. 


CHAP.  VIII. 


experiments.  Short  bars  are  known  to  give  a  higher  average  tenacity  than  long  bars. 
Now,  a  bar  with  a  hole  drilled  in  it  is  virtually  a  very  short  bar,  and  it  ought,  there- 
fore, if  there  were  no  cause  of  diminution  of  strength,  to  show  a  higher  tenacity  than 
ordinary  test-bars.  But,  in  fact,  there  is  generaUy  a  loss  of  strength. 

"In  some  experiments  there  is  a  curious  apparent  increase  of  strength  after  drilling. 
Thus,  in  one  of  Mr.  Stoney's  experiments  the  drilled  plate  was  7J  per  cent,  stronger 
than  the  undrilled  plate.  In  some  experiments  by  Mr.  Parker  the  plain  plate  carried 
26.4  tons,  while  a  plate  punched  and  annealed  carried  31.7  tons.  See  also  the  table  of 
treble-riveted  joints  given  further  on.  (Section  15  of  the  present  chapter.)  Mr.  Adam- 
son  also  finds  that  the  tenacity  through  a  line  of  drilled  holes  is  a  little  greater  than  the 
tenacity  of  the  plate  before  drilling.  Discrepancies  of  this  kind  may  be  due  to  the 
holes  causing  fracture  at  a  section  stronger  per  square  inch  than  other  parts  of  the 
plate.  An  ordinary  test-bar  breaks  at  the  weakest  part  of  a  more  or  less  considerable 
length  of  bar. 

"  (3.)  If  the  material  in  the  neighborhood  of  the  surface  of  fracture  is  initially  (before 
the  application  of  the  load)  in  an  irregularly-strained  condition,  or  has  in  different 
parts  unequal  power  of  elongating,  then  the  stress  will  not  be  uniform  at  the  moment  of 
fracture,  and  the  apparent  tenacity  will  be  less  than  the  real  tenacity.  This  is  the 
cause  of  the  loss  of  strength  due  to  punching.  By  the  action  of  the  punch  metal  is 
caused  to  flow  laterally  into  the  surrounding  metal.  This  induces  initial  stresses  in  an 
annulus  of  metal  round  the  hole,  and  very  probably  also,  as  M.  Barba  thinks,  alters  its 
power  of  elongation.  If  the  power  of  elongating  is  diminished  in  part  of  the  metal, 
that  part  gets  an  excessive  proportion  of  the  load  and  breaks  before  the  rest  is  fully 

strained.  The  result  of  either  loss  of 
tenacity  or  loss  of  ductility  is  to  di- 
minish the  apparent  tenacity  of  the 
metal  to  an  extent  which  certainly 
reaches  in  some  cases  20  to  30  per  cent. 
Figure  51  shows  a  possible  condition  of 
the  bar  after  punching,  the  ordinates 
of  the  dotted  curves  representing  the 
stresses.  Immediately  round  the  hole 
is  an  annulus  in  which  the  stress  is 
compressive,  the  compression  being  due 
to  material  forced  in.  To  balance  the  forces  in  this  ring  an  annulus  in  which  the  stress 
is  tension  must  surround  it. 


Fig.  51. 


SEC.  12. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


183 


"In  some  experiments  there  appears  to  occur  a  serious  diminution  of  the  apparent 
tenacity  in  riveted  joints  when  the  bearing-surface  of  the  rivets  on  the  plates  is  too 
small,  and  when  consequently  the  crushing  pressure  between  the  rivet  and  plate  is  ex- 
cessive. It  is  possible  that  this  is  due  to  an  action  like  that  which  occurs  in  punching. 
The  pressure  of  the  rivet  may  cause  a  lateral  flow  of  the  metal,  and  alter  either  the 
stress  or  the  elasticity  of  a  ring  of  metal  round  it.  The  stress  on  the  tearing  section 
being  then  unequal,  a  low  apparent  tenacity  is  found."  (First  Report  of  the  Commit- 
tee of  the  Institution  of  Mechanical  Engineers  on  the  Form  of  Riveted  Joints.} 

In  multiple-riveted  joints  of  materials  of  different  elasticities — e.g.,  steel  andiron,  or 
cast  and  wrought  iron — the  outermost  row  of  rivets  has  to  bear  the  greater  stress.  If 


Fig.  52. 


' 


the  elastic  rod  S  (figure  52)  is  riveted  to  a  non-elastic  body, 
K,  by  several  rows  of  rivets,  the  row  1  must  bear  the  entire 
stress  B,  for  the  part  of  B  assigned  to  2  must  act  by  tension 
on  1  2,  tending  to  stretch  it.  Since  1  does  not  yield,  on  ac- 
count of  the  deficient  elasticity  of  K,  the  part  of  B  assigned  2 
is  transferred  back  to  1  by  compression. 

If  two  bodies,  whose  elongations  for  the  same  stress  are 
nearly  equal,  are  riveted  double  or  triple  they  strive  to  attain 
unequal  elongations  between  rivets,  because  the  forces  acting 
on  the  adjacent  parts  are  not  equal.  Denote  the  total  tension 
on  the  joint  by  B,  the  stresses  on  the  rivets  (figure  53)  by 
I,  n,  III,  and  I',  II',  III',  and  the  stresses  on  the  interme- 
diate portions  of  the  plates  by  I  H,  II  III,  and  I'  II',  II'  HI', 
then 


i  ii  =  T  IT  =  B  -  1 

II  =  II'  and  III  =  HI' 
II  HI  =  II'  III'  =  B  -  I  -  H 

The  parts  I  II  and  II'  III'  are  therefore  under  the  action  of  forces  of  different  magni- 
tudes —  viz.,  B  —  I  and  B  —  I  —  II.  The  rivet  I  cannot  yield  to  the  elongation  of  I  II, 
and  a  portion  of  this  force  must  act  as  pressure  on  I.  The  same  holds  true  of  the  por- 
tions II  III,  I'  II',  and  the  rivet  I'. 

Hence  the  weak  point  of  every  riveting  which  is  more  than  double  lies  near  the 
outermost  rivet  in  the  direction  of  the  strain.  (  Weyrauch,  '  Strength  of  Iron  and  Steel 
Construction.') 

12.  Strength  of  Materials  in  Riveted  Joints.  —  The  tensile  strength  of  boiler- 


184  STEAM  BOILERS.  CHAP.  VI1L 

plates  at  the  joints  per  square  inch  of  section  is  generally  less  than  that  of  the  original 
plates  ;  but  this  loss  of  tenacity  varies  according  to  the  treatment  received  by  the  plates 
in  the  process  of  construction.  When  the  rivet-holes  are  drilled  the  strength  of  the 
material  is  not  diminished  to  an  appreciable  extent.  When  the  holes  are  punched  the 
loss  of  tenacity  varies  with  the  form  of  punch  used  and  with  the  quality  of  the  mate- 
rial ;  it  is  greater  for  hard  than  for  very  ductile  materials,  and  is  generally  greater  for 
steel  than  for  iron ;  it  increases  with  the  thickness  of  the  plates,  and  as  the  diameters 
of  the  punch  and  of  the  die-hole  are  more  nearly  alike.  Experiments  on  punched  iron 
plates  show  a  loss  of  tenacity  varying  from  5  to  20  per  cent,  of  the  original  strength  of 
the  plates.  In  steel  plates  punching  produces  a  loss  of  tenacity  varying  from  8  to  35 
per  cent,  of  the  original  strength  ;  but  the  plates  can  be  restored  to  their  original  tena- 
city by  annealing  them  after  punching,  or  by  reaming  out  the  punched  holes.  (See  sec- 
tion 5  of  the  present  chapter.) 

In  an  experiment  made  by  Adamson  the  strength  of  a  perforated  bar  was  increased 
5.8  per  cent,  by  driving  a  turned  pin  into  the  hole,  so  as  to  prevent  the  metal  round  the 
hole  from  collapsing  into  an  elliptical  shape ;  thus  producing  more  nearly  the  same  con- 
dition as  obtains  in  riveted  joints. 

It  is  generally  assumed  that  the  shearing  strength  of  wrought-iron  is  80  per  cent. 
of  its  tensile  strength,  if  the  shear  is  in  a  plane  perpendicular  to  the  direction  of  rolling, 
and  if  the  tension  is  applied  parallel  to  the  direction  of  rolling.  In  a  paper  on  the 
strength  and  proportions  of  riveted  joints,  by  W.  R.  Browne,  communicated  to  the 
Institution  of  Mechanical  Engineers  in  1872,  it  is  assumed  that  the  shearing  resistance 
of  iron  rivets 

in  single-shear  is 22  tons  per  square  inch. 

in  double-shear  is 21        "  " 

Some  of  Fairbairn's  experiments  on  the  shearing  resistance  of  rivets  gave  the  following 
results : 

Eivet-holes  drilled,  edges  of  holes  sharp 19.23  tons  per  square  inch. 

Rivet-holes  drilled,  edges  of  holes  rounded 21.52        "  " 

Rivet-holes  punched 20.95        "  " 

Experiments  made  by  David  Greig  and  Max  Eyth  on  Taylor's  Yorkshire  rivet-iron 
and  Brown  &  Co.'s  mild  rivet-steel  gave  for  the  tensile  strength  of  the  iron  22.2  tons  per 
square  inch,  and  of  the  steel  28.8  tons  per  square  inch.  The  shearing  resistance  of  the 
iron  was  19  tons,  and  that  of  the  steel  22.1  tons.  Some  plates  riveted  together  were 
then  tested,  and  a  somewhat  higher  shearing  resistance  was  found  than  for  bars  not 
formed  into  rivets.  This  is  ascribed  partly  to  the  rivet  being  increased  in  diameter  to 


SBC.  12.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  185 

fill  a  hole  larger  than  its  normal  size,  partly  to  the  friction  of  the  plates.  The  harden- 
ing of  the  rivet  is  a  possible  cause  of  increased  resistance  of  rivets  as  compared  with 
simple  bars. 

The  crushing  pressure  of  the  rivet  on  the  plate  is  discussed  by  Professor  W.  C. 
Unwin  in  the  '  First  Report  of  the  Committee  of  the  Institution  of  Mechanical  Engi- 
neers on  the  Form  of  Riveted  Joints,'  as  follows: 

"  If  F  is  the  tension  on  a  joint  corresponding  to  one  rivet, 
d      the  diameter  of  the  rivet,  and 
t      the  thickness  of  the  plate, 

then  C  =  £    [I.] 

may  be  denned  as  the  mean  crushing  pressure  of  the  rivet  on  the  plate. 

"Putting  Sfor  the  shearing  resistance  of  the  rivet,  then,  the  rivets  being  in  single 
shear, 


-      =  .786  -,  [II.] 

or  the  crushing  pressure  is  greater  as  the  ratio  of  the  rivet  diameter  to  the  thickness  of 
plates  is  greater. 

"This  is  sometimes  given  as  the  reason  why  the  rivet  diameter  should  not  exceed 
2£  to  3  times  the  plate  thickness.  It  is  by  some  writers  asserted  that  if  in  any  case 
C  is  more  than  30  or  40  tons  per  square  inch  for  iron  joints,  then  the  joint  gives  way 
with  a  very  low  apparent  tenacity.  During  the  application  of  the  load  the  rivet-hole 
becomes  oval,  the  metal  of  the  plate  is  crushed  and  its  tenacity  diminished.  The  pre- 
cise way  in  which  the  crushing  affects  the  tenacity  has  not  hitherto  been  indicated  ; 
but  it  is  suggested  above  (see  section  11  of  the  present  chapter}  that  it  produces  an 
unequal  distribution  of  the  stress  similar  to  that  induced  by  punching.  There  are  no 
direct  experiments  on  the  crushing  of  iron  and  steel  which  are  of  any  value  in  deter- 
mining the  proper  limits  of  crushing  pressure  for  riveted  joints.  .  .  . 

"From  the  very  irregular  distribution  of  the  pressure  on  the  surface  of  the  rivet  it 
is  probable  that  the  maximum  pressure  of  the  rivet  on  the  plate  is  much  greater  than 
its  mean  value  C." 

A  mathematical  investigation  of  the  stresses  indicates  that  the  maximum  crushing 
pressure  is  1.27  times  the  mean  crashing  pressure,  but  the  writer  is  of  the  opinion  that 
in  practice  the  value  of  the  maximum  crushing  pressure  is  much  greater,  especially  with 
rivets  in  single  shear. 


186 


STEAM  BOILERS. 


CHAP.  VIII. 


Discussing  some  results  obtained  with  actual  joints  which  have  a  bearing  on  this 
question,  he  finds  that  there  seems  to  be  a  tolerably  regular  increase  of  apparent  tena- 
city as  the  crushing  pressure  diminishes,  and  that  the  diminution  of  tenacity  is  sen- 
sible in  lap-joints  where  the  crushing  pressure  exceeds  30  tons,  and  was  very  great  in 
some  cases  where  the  crushing  pressure  reached  40  tons.  These  remarks  apply,  how- 
ever, only  to  iron  lap-joints.  Experiments  with  butt-joints  show  great  anomalies. 

"With  steel  joints  also,  even  with  very  high  crushing  pressures,  no  regular  effect 
on  the  tenacity  is  traceable.  It  seems  possible  to  the  reporter  that  the  explanation  of 
these  anomalies  may  be  found  in  the  variation  of  the  relative  hardness  of  the  rivets  and 
plate.  If  the  rivet  is  sensibly  harder  than  the  plate,  the  plate  will  suffer ;  but  if  the 
rivet  is  sensibly  softer  than  the  plate,  the  rivet  will  suffer.  With  iron  plates  some- 
times the  rivet  and  sometimes  the  plate  is  the  harder.  With  steel  the  rivet  appears  to 
be  generally  softer  than  the  plate.  It  must  be  borne  in  mind  that  this  suggestion  is 
only  offered  as  a  conjectural  explanation  of  anomalies  which,  unless  they  are  due  to 
errors  in  the  experiments,  are  extremely  puzzling." 

13.  Proportioning  Riveted  Joints. — A  riveted  joint  subjected  to  tension  can 
break  — 

(1)  By  the  tearing  of  the  plate  ;  in  this  case  its  strength  is  measured  by  the  tensile 
strength  of  the  plate  multiplied  by  its  least  sectional  area,  which  obtains  on  a  line  pass- 
ing through  the  rivet-holes,  and  depends  upon  the  thickness  of  the  plate  and  the  diame- 
ter and  spacing  of  the  rivets  ; 

(2)  By  the  shearing  of  the  rivets  ;  in  this  case  its  strength  is  measured  by  the  shear- 
ing strength  multiplied  by  the  sectional  area  of  the  rivets  ; 

(3)  In  consequence  of  the  thrust  exerted  by  the  rivets  on  the  plate,  which  may  cause 
it  either  to  be  crushed  (figure  54),  or  to  split  (figure  55),  or  to  have  a  portion  sheared 

Fig.  54. 


Fig.  55. 


Fig.  56. 


out  (figure  56)  from  the  rivet-holes  to  the  edge  of  the  plate ;  and  in  this  case  the 
strength  of  the  joint  depends  on  the  diameter  of  the  rivets,  the  thickness  of  the  plate, 


SEC.  13.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  187 

the  width  of  the  lap,  and  a  coefficient  of  resistance  depending  on  the  nature  of  the 
fracture.  The  shearing  of  the  plate  from  the  rivet-holes  to  the  edge  is,  however,  not 
likely  to  take  place  with  the  ordinary  proportions  of  lap  and  rivets. 

The  thickness  of  the  plates,  the  diameter  and  spacing  of  the  rivets,  and  the  width  of 
the  lap  must  be  proportioned  in  such  a  manner  that  the  strength  of  the  joint  approaches 
as  nearly  as  possible  the  strength  of  the  whole  plate,  and  that  the  same  liability  exists 
for  the  different  kinds  of  fracture  to  take  place  ;  at  the  same  time  the  tightness  of  the 
joint  and  facilities  of  construction  have  to  be  taken  into  consideration. 

Assuming  that  the  average  shearing  strength  of  iron  rivets  is  19  tons  per  square  inch, 
and  that  the  crushing  pressure  of  the  rivets  on  the  plates  should  not  exceed  30  tons 
per  square  inch  (see  sections  11  and  12  of  the  present  chapter),  we  can  find  the  proper 
diameter  of  a  rivet  for  a  given  thickness  of  plates  by  introducing  these  values  into  for- 
mula [//.]  of  section  12  of  the  present  chapter,  viz.: 


-  -        . 

S       19  t 

consequently  d  =  2  1, 

for  joints  in  which  the  rivets  are  in  single-shear. 

When  the  rivets  are  in  double-shear  they  will  bear  about  90  per  cent,  more  than  the 
same  rivets  in  single-shear,  and  under  these  conditions  equation  [II.  ]  assumes  the  fol- 
lowing form,  viz.  : 

Odt  =  1.908—  ff; 
4 

hence  .£=»=!.«.£ 

consequently  d  =  1.05  t. 

In  practice,  when  the  rivets  are  in  single-shear,  d  is  generally  made  equal  to  2  t  for 
plates  up  to  f  inch  thick.  But  this  proportion  is  gradually  decreased  for  thicker 
plates,  because  the  formula  d  —  2t  would  give  rivets  of  so  large  a  diameter  that  they 
could  not  be  spaced  close  enough  to  make  a  steam-tight  joint  and  at  the  same  time 
make  the  plates  and  rivets  of  equal  strength  ;  and,  when  the  thickness  of  the  plates 
exceeds  ^  inch,  the  rivets  would  become  so  large  that  they  could  not  be  properly 
worked  down.  In  boiler-making  rivets  exceeding  l£  inches  in  diameter  are  rarely  used. 

When  the  plates  to  be  connected  are  of  unequal  thickness  the  diameter  of  the  rivets 
is  proportioned  to  the  thicker  plate.  When  more  than  two  plates  are  to  be  connected 
the  diameter  of  the  rivets  is  increased  by  about  one-eighth  inch. 

For  steel  boiler-plates  it  is  better  to  use  steel  rivets  than  iron  xivets,  which  should 


188 


STEAM  BOILERS. 


CHAP.  VIII. 


Fig.  57. 


be  of  somewhat  smaller  diameter  in  proportion  to  the  thickness  of  the  plates,  and 
spaced  correspondingly  closer,  than  iron  rivets  with  iron  boiler-plates. 

The  diameter  of  the  rivets  being  determined  by  the  thickness  of  the  plates,  it  is  con- 
venient to  express  the  pitch  of  the  rivets  and  the  width  of  the  lap  in  terms  of  the 
diameter  of  the  rivets. 

The  width  of  the  lap,  measured  from  the 
centre  of  the  rivet-hole  to  the  edge  of  the 
plate,  has  been  fixed  practically  at  1.5  d. 

(This  gives  ample  strength  to  resist  the  thrust 
of  the  rivet,  and  makes  a  proper  allowance 
for  calking;  too  large  a  lap  does  not  make 
a   tight    joint,  since  the  sheets  are    apt  to 
be   forced   apart   by  '  severe    calking   (figure 
57).    • 

14.   Lap-joints.  —  The  single-riveted  lap-joint  requires  less^  labor  and  material 
than  any  other  riveted  joint  ;  but  its  strength,  compared  with  that  of  the  solid  plate,  is 
small,  because  the  sectional  area  of  the  plate  in  the-  line  of  rivets  is  greatly  reduced, 
and  on  account  of  the  unequal  distribution  of  the  stresses.     In  boilers  this  joint  is  used 
especially  in  the  furnaces  and  back-connections,  where  it  is  advantg,gedBMmake  the 
lap  as  narrow  as  possible,  and  in  those  parts  which  are  not  subjected 
and  where  great  strength  and  tightness  are  not  required,  as  for 
connections,  etc. 

Calling  the  total  tensile  force  applied  to  a  single-riveted  joint 

the  ultimate  tensile  strength  of  the  plate  per  unit  of  area  ..........  T, 

the  ultimate  shearing  strength  of  the  rivets  per  unit  of  area  ........  S; 

and  representing  the  number  of  rivets  in  the  joint  by  ..............  n, 

» 

their  diameter  by  ............  ..................................  d, 

the  thickness  of  the  plates  by  ..................  ...............  .  .  t, 

the  pitch  of  the  rivets  by  ....................  *  .....  ..............  p, 

we  can  express  the  width  of  the  joint  by  .........................  np. 

The  dimensions  of  the  rivets  and  of  the  plate  being  so  proportioned  that  they  offer 
equal  resistance  to  F,  and  supposing  this  stress  to  be  borne  equally  by  every  part  of  the 
plate  in  proportion  to  its  sectional  area,  we  have  the  equation  : 

F=nd*  .7854  8=n(p  —  d)t  T; 


ressure 


giptakes, 


$.  .  . 


and 


p  =  d?  .7854 


, 

t 


d. 


SEC.  14. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


189 


Since,  with  the  dimensions  ordinarily  used  in  boiler-making,  the  value  of  d  varies  be- 
tween 2 1  and  1.5 1,  the  values  of  p  lie  between  d  ( 1+ 1.5708  ^  \  and  d  (l  +  1.1781-^Y 

In  using  these  formulae  for  calculating  the  value  of  p  we  must  insert  for  T  and  8 
the  values  of  the  apparent  tensile  and  shearing  strengths  of  plates  and  rivets  in  single- 
riveted  lap-joints,  as  found  by  experiment.  (See  section  15  of  the  present  chapter.} 
The  sectional  area  of  the  plates  in  a  boiler  is  reduced  continually  by  corrosion,  while 
the  shank  of  the  rivet  remains  intact.  This  action  must  be  taken  into  account  in  pro- 
portioning a  joint. 

D.  K.  Clark  says  that  "the  shearing  section  of  rivets  should  not  in  any  case  exceed 
the  net  section  of  the  plate,  and  that  the  maximum  strength  of  joint  is  attainable  when 
the  shearing  section  is  from  90  to  100  per  cent,  of  the  net  section  of  the  plate."  Making 
the  area  of  the  rivets  90  per  cent,  of  the  net  section  of  the  plate,  the  value  of  p,  for 
d  =  2t,  becomes  j?  =  2.745d;  and  for  d  =  1.5 t,  p  —  2.309  d.  These  values  do  not  differ 
much  from  ordinary  practice. 

The  double-riveted  lap-joint  is  from  20  to  33  per  cent,  stronger,  and  is  more  easily 
kept  tight,  than  the  single-riveted  joint.  It  is  used  most  extensively  for  steam-tight 
joints  which  do  not  come  in  contact  with  the  fire  and  hot  gases. 

Retaining  the  notation  given  above,  we  have  the  equation : 


™ 


.  78548=     (p-d)tT; 

& 


Fig.  58. 


Fig.  59. 


and  p  =  d1 

Making  the  area  of  the  rivets  90  per  cent,  of  the  net  section  of  the  plate,  the  value 
of  p,  for  d  =  2t,  becomes 

p  =  4. 4907  tf; 
and  for  d  =  1.5 1,  p  =  3.618  d. 

The  rivets  of  a  double-riveted  joint  in 
boilers  are  generally  placed  in  a  zigzag  line. 
Some  of  Brunei's  experiments  show  that 
when  the  rows  of  rivets  are  too  close  the  line 
of  fracture  is  a  zigzag,  running  backward 
and  forward  between  the  rows  (figures  58 
and  59),  and  a  much  greater  section  of 
metal  is  divided  than  if  the  fracture  took 


place  on  a  line  passing  through  the  centre  of  the  rivet-holes  in  either  row.      This  is 
explained  by  the  fact  that  punching  weakens  the  sheet  to  some  distance  around  the 


190  STEAM  BOILERS.  CHAP.  V11I. 

hole,  and  that  the  amount  of  this  weakening  effect  on  the  area  represented  by  the 
zigzag  line  is  twice  as  great  as  that  on  the  area  represented  by  the  straight  line  be- 
tween two  contiguous  holes  in  the  same  row,  as  has  been  illustrated  by  the  shading 
around  the  holes.  Brunei  found  that  the  distance  between  the  two  rows  of  staggered 
rivets  should  be  two-thirds  of  the  pitch  of  the  rivets. 

In  chain-riveting  it  is  safe  to  make  the  distance  between  the  centre  lines  of  the  rows 
of  rivets  equal  to  2£  diameters  of  the  rivets. 

Treble  and  quadruple  riveted  lap-joints  are  sometimes,  but  rarely,  used  for  the 
shell  of  cylindrical  boilers.  With  plates  of  ordinary  thickness,  in  which  the  diameter 
of  the  rivets  is  from  1£  to  2  times  the  thickness  of  the  plates,  multiple-riveting  makes 
the  pitch  of  the  rivets  so  large  that  the  joint  cannot  well  be  calked  steam-tight.  This 
objection  does  not  exist  in  the  case  of  thick  plates,  in  which  the  diameter  of  the  rivets 
exceeds  but  little  or  nothing  the  thickness  of  the  plates.  The  increase  of  strength  ob- 
tained by  increasing  the  rows  of  rivets  is,  however,  not  proportionate  to  the  additional 
labor  and  material  required  for  making  the  joint,  on  account  of  the  very  unequal  dis- 
tribution of  the  stresses.  (See  section  11  of  the  present  chapter.)  The  dimensions  of 
multiple  joints  may  be  calculated  by  formulae  similar  to  those  given  for  single  and 
double  riveted  lap-joints,  introducing  for  S  and  T  the  values  given  in  Table  XXVI. 

15.  Experiments  on  the  Strength  of  Lap-joints. — The  experiments  made  by 
Fairbairn  in  1838  have  served  up  to  the  present  time  as  the  basis  for  calculating  the 
strength  of  riveted  joints.  According  to  these  experiments  the  strength  of  a  double- 
riveted  joint  is  70  per  centum  of  the  strength  of  the  plate,  and  of  a  single-riveted  joint 
56  per  centum.  Of  these  experiments  it  is  necessary  to  remark : 

1st.  That  the  results  are  only  for  the  case  in  which  the  rivet-holes  diminish  the  sec- 
tion of  the  plate  30  per  centum,  while  for  the  most  part  in  practice,  and  particularly 
for  the  single-riveted  joint,  that  loss  is  very  much  greater. 

2d.  That  the  experiments  were  made  on  plates  of  only  0.224  inch  thickness. 

3d.  That  the  experiments  gave  46,  and  not  56,  per  centum  for  the  strength  of  the  sin- 
gle-riveted joint ;  the  coefficient  was  arbitrarily  increased  by  Fairbairn  to  cover  certain 
imperfections  in  the  experiments. 

This  increase  was  partly  made  for  the  purpose  of  allowing  for  the  increase  of 
strength  given  to  riveted  joints  by  arranging  contiguous  plates  in  such  a  manner  that 
their  joints  do  not  lie  in  the  same  line  ;  but  the  increase  of  strength  due  to  this  arrange- 
ment is  much  greater  with  narrow  plates,  such  as  were  formerly  in  general  use,  than 
with  wide  plates,  such  as  are  nowadays  manufactured. 

Experiments  on  various  plate-joints  made  by  W.  Bertram  at  Woolwich  Dockyard 


SEC.  15.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  191 

I 

were  published  and  discussed  in  1860  by  D.  K.  Clark.  The  thicknesses  of  the  plates 
were  f  inch,  T\  inch,  and  £  inch,  and  in  the  single-riveted  joint  the  net  sectional  area  of 
the  plates  in  the  line  of  rivets  was  62.5  per  cent,  of  the  solid  plate.  The  relative 
strength  of  the  joints  of  the  f-inch  plate  is  given  by  him  as  follows : 

Entire  plate 100 

Double-riveted  joint 72 

Single-riveted  joint 60 

He  found  that  in  the  f-inch  plate  the  tensile  strength  per  square  inch  of  net  section 
of  the  single-riveted  joint  was  nearly  equal  to  that  of  the  entire  plate,  while  in  the  ^V- 
inch  plate  it  was  only  four-fifths,  and  in  the  £-inch  plate  two-thirds,  of  the  strength  of 
the  entire  plate,  so  that  the  joint  of  the  thinner  plates  was  actually  stronger  than  that 
of  the  thicker  plates.  This  remarkable  reduction  of  strength  in  thick  plates  is  as- 
cribed to  the  distorting  leverage  of  the  lap,  which  increases  with  the  thickness  of  the 
plates.  Figure  46  shows  the  ultimate  distortion  of  lap-joints  by  the  oblique  action  of 
the  tension.  The  decrease  of  strength  with  the  thickness  of  the  plates  in  these  experi- 
ments is,  however,  much  greater  than  has  been  found  in  more  recent  experiments,  and 
the  strengths  of  the  riveted  joints  of  the  f-inch  plates,  as  given  above,  are  likewise 
greatly  in  excess  of  the  average  results  of  experiments. 

Clark  found  also  that  countersunk  riveting  did  not  impair  the  strength  of  the  joint 
as  compared  with  external  heads,  which  result  he  explains,  likewise,  by  the  oblique 
stress  on  the  lap-joint.  He  says  :  "  On  the  principle  here  noticed  one  may  account  for 
the  practically  equal  strength  of  the  joints  made  with  countersunk  rivets,  compared 
with  those  having  external  rivet -heads,  notwithstanding  the  greater  reduction  of  solid 
section  by  countersinking :  the  leverage  is  shortened  and  it  may  be  measured  from  the 
Fig.  60.  centre  of  the  cylindrical  part  of  the 

~J rivet  in  the  line  a  b  (figure  60),  or 

I  thereabouts,  toward  the  inner  side 
of  the  plate.  On  the  same  princi- 
ple the  conical  form  of  punched  holes  reduces  the  leverage  and  the  obliquity  of  the 
pulling  stress." 

In  the  above-mentioned  '  First  Report  of  the  Committee  of  the  Institution  of  Me- 
chanical Engineers '  the  most  reliable  experiments  on  riveted  joints  have  been  tabu- 
lated, all  experiments  being  omitted  in  which  the  crushing  pressure  of  the  rivets  on 
the  plate  was  so  great  as  probably  to  have  affected  in  a  considerable  degree  the  appa- 
rent tenacity  of  the  joint.  The  ratio  of  the  tension  on  the  joint  to  the  area  of  the  sec- 


192  STEAM  BOILERS.  CHAP.  VIII. 

tion  at  the  place  of  fracture  is  called  the  apparent  tenacity  of  the  joint,  which  is  ren- 
dered less  than  the  original  tenacity  of  the  iron  by  any  injury  done  in  drilling  or  punch- 
ing, and  by  the  irregularity  of  stress  due  to  the  crushing  action  between  the  rivets  and 
plates,  and  by  the  irregular  distribution  of  stress  due  to  bending  of  the  joint  under  the 
action  of  the  load,  etc. 

From  a  large  number  of  experiments  on  single-riveted  lap-joints  of  iron  plates  it 
appears  that  the  apparent  tenacity  of  the  plate  in  this  joint  is  from  20  to  32  per  cent, 
less  than  that  of  the  original  plate,  with  punched  holes,  and  about  12  per  cent,  less  with 
drilled  holes.  Since  iron  plates  do  not  receive  any  appreciable  injury  in  drilling,  this 
loss  in  tenacity  of  12  per  cent,  has  to  be  ascribed  mainly  to  the  irregular  distribution  of 
the  stress. 

The  mean  shearing  resistance  of  the  rivets  is  about  6  per  cent,  greater  in  punched 
holes  than  in  drilled  holes.  With  punched  holes  the  ratio  of  the  apparent  tenacity  of 
the  plates  to  the  shearing  resistance  of  the  rivets  is  85  to  100,  but  with  drilled  holes  the 
plates  are  stronger  per  unit  of  area  than  the  rivets  in  the  ratio  of  107  to  100. 

The  mean  efficiency  of  the  single-riveted  lap-joint,  in  per  cent,  of  the  tenacity  of  the 
solid  plate,  is  44.6  per  cent,  when  the  holes  are  punched  and  50  per  cent,  when  the  holes 
are  drilled. 

The  mean  results  of  nine  experiments  with  double-riveted  lap-joints  of  iron  plates 
with  punched  holes  give  an  apparent  tenacity  of  the  plate  of  89.5  per  cent.,  and  an 
efficiency  of  the  joint  equal  to  59  per  cent,  of  the  tenacity  of  the  solid  plate. 

Two  experiments  with  drilled  iron  plates  and  double-riveted  lap-joints,  by  Greig  and 
Eyth,  give  a  mean  apparent  tenacity  of  95  per  cent,  and  a  mean  efficiency  of  joint  of  61 
per  cent. 

Several  experiments  with  double-riveted  lap-joints  of  punched  iron  plates  1  inch  and 
|  inch  thick,  made  by  Kirkaldy  for  R.  V.  J.  Knight,  gave  remarkably  low  results. 
The  mean  apparent  tenacity  of  the  plates  at  the  joint  was  only  56.4  per  cent,  of  the 
tenacity  of  the  solid  plate  ;  and  the  mean  of  four  experiments  with  1-inch  plates  gave 
34.5  per  cent.,  and  the  mean  of  two  experiments  with  f-inch  plates  gave  42.6  per  cent., 
for  the  efficiency  of  the  joint.  This  great  reduction  of  strength  appears  to  have  been 
due  to  the  unequal  distribution  of  the  stress  in  consequence  of  the  bending  of  the 
joint  under  the  action  of  the  load,  since  two  similar  iron  plates,  1  inch  thick,  with 
punched  holes,  but  forming  a  double-riveted  butt-joint  with  double  covering-plates, 
which  were  tested  by  the  same  parties,  gave  an  apparent  tenacity  of  90  per  cent,  of 
the  tenacity  of  the  solid  plate. 

The  average  values  of  a  number  of  experiments  with  double-riveted  steel  lap-joints 


SEC.  15. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


193 


make  the  apparent  tenacity  of  the  plates  at  the  joint  from  4  to  8.5  per  cent,  greater 
than  the  tenacity  of  the  solid  plate,  and  21  per  cent,  greater  than  the  shearing  resistance 
of  steel  rivets  per  square  inch  of  sectional  area. 

Table  XXVI.  contains  the  results  of  experiments  with  treble  and  quadruple  riveted 
lap-joints  made  of  steel  plates  with  steel  and  iron  rivets,  and  is  compiled  principally 
from  the  '  First  Report  of  the  Committee  of  the  Institution  of  Mechanical  Engineers 
on  the  Form  of  Riveted  Joints.'  The  joints  were  made  partly  by  Denny  &  Co.,  of 
Dumbarton,  and  the  specimens  were  tested  by  Kirkaldy.  The  stresses  corresponding 
to  the  actual  mode  of  fracture  of  the  joints  are  printed  in  heavy  type;  the  other 
stresses,  printed  in  ordinary  type,  are  those  which  obtained  at  the  moment  of  frac- 
ture, but  are  lower  than  those  at  which  the  joint  would  have  given  way  by  the  respec- 
tive modes  of  fracture.  The  joints  marked  a,  b,  and  c  in  the  table  and  their  lines  of 
fracture  are  represented  in  figures  61,  62,  and  63  respectively.  The  steel  plates  had  a 


Fig.  61, 


Fig,  62. 


Fig.  63. 


T~ 

th- 


nominal  thickness  of  |  inch,  and  the  steel  rivets  had  a  diameter  of  1.13  inches.  The 
tensile  strength  of  the  rivets  in  these  four  joints  was  28.9  tons  per  square  inch,  and 
their  apparent  shearing  strength  varied  consequently  from  66.5  to  71.4  per  cent,  of  their 
tenacity. 


194 


STEAM  BOILERS. 


CHAP.  VIII. 


TABLE    XXVI. 

RESULTS  OF  EXPERIMENTS  WITH  TREBLE  AND  QUADRUPLE-RIVETED  LAP-JOINTS. — STEEL  PLATES. 

TESTED  BY  KIRKALDY. 


Mode 
of  riveting. 

Holes. 

!§r 

i 

•gg 

J 

•S£js 

rt  rt  o 

J3J 

Stress  at  moment  of  fracture,  in 
tons  per  square  inch. 

Apparent  tenacity  of 
plate  at  joint  in  per 
cent,  of  tenacity  of 
solid  plate. 

Efficiency  of  joint. 

Thickness  of  plate. 

Rivets. 

Tensile. 

Shearing. 

Crushing. 

Treble-riveted  

31-2 

28.8 
30.9 
30.4 
31.2 

31.6 

32.7 
28.3 
28.2 
31.6 
29.1 
28.6 
27.7 
27.1 
31-7 
29.1 
3°4 
27.5 
27.4 
27-3 
27-4 
30-7 
32.2 
28.8 
28.8 
27.6 
28.0 
30.0 
26.7 

23.34 
22.47 
36.11 
35.00 
35.38 
32.75 
31.27 
29.88 
30.14 
35.88 
33.83 
30.47 
29.44 
25.34 
32.30 
29.89 
25.89 
26.07 

J9-74 
21.41 

25-91 
34.76 
34-95 
31.92 
31.84 
26.42 
29.22 

25-55 
28.16 

I2.O 
12.2 

16.1 

15.6 

18.2 

17.6 
16.5 
15.7 

15.8 

23-3 

22.O 
22.2 

21-5 
18.4 

25.1 
25.5 
23.9 
24.1 
19.4 
20.6 
19.2 
19.1 
19.2 
17.4 
17.4 
16.7 
15.2 
16.5 
15.9 

17-58 
16.85 
24.32 
23-57 
26.79 
25.76 

24.59 
23.31 

23-51 
32.96 

22.IO 
21.24 
15.83 
18.91 
3&.OI 
25.IO 

23.14 
20.54 
19.63 
21.25 

I9.5I 
27.03 
27.12 

23-93 
23.88 
2O.80 
2O.22 
2O.  I  O 
20.12 

75 
78 
H7 
"5 
"3 
104 
96 
106 
107 

H4 

116 
107 
106 
94 

52 
54 
77 
76 

79 
73 
67 
74 
75 
83 
77 
72 
69 
70 
79 
73 
62 

67 
54 
59 
71 
79 
76 

77 
77 
67 
70 
60 
7i 

1  in. 

,it   «< 

i  6 

i  .'.' 

1  ;; 

*  " 
i  ;; 

j_    « 

4 

1   " 

i 

!  " 
I  ;; 

i   " 
\  ;; 

M 

i  ;; 

«  " 

*  •• 

i  " 

a.    <« 

4 

1   " 

Iron. 
Steel. 

II 

Steel. 

VI 

(1 

Iron, 
it 

u 
11 

M 

1  t 

Drilled  

<i 

(i 

ft 

<  i 

K 

ii 

« 

i 

4< 

, 

M 

i 

Treble-chain  

< 

(1 

i 

M 

i 

1  1 

i 

Quadruple-zigzag  (<:). 

Punched  and  reamed. 
Drilled  

ii 

u 

(i 

« 

Treble-zigzag  (a)  
Treble-zigzag  (a)..  .  . 
?uadruple-zigzag  (£). 

Drilled  and  reamed.. 

Punched  and  reamed. 
K                «i 

Drilled  

II 

(4 

I 

I 

I 

I 

1 

LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


195 


x 


tn 

•x 

l-t 

O 


w 

w 


in 

2 
O 


O 

B. 

O 
B! 

- 


-dcus     qlu» 


•  juiod  spins 


•s».iu  jo  xsuoiEia 


•B  -I»AUJO 

" 

SO  I 


•S»AU  jo  notuna 


TOAUjoqDlM  S 


%  uci|4  .iv^jiifi  lou  speajj 


•conannp  ^C  urqi  sss|  105; 


-tip  jnoj 


joa  93jtji  ireqi 


JOJ.J 


I 


1 


•s 


»;  at  «  st 

MMHM 

222S 


3!  »  at       x 

nnncoM 

22222 


,  5 


S3U111  £-t    UEql   3JOU1  J3A3U  puE  '  J3  J3OTBIp  3q)  SStnll  £ 


J! 
I 


•S»AU  JO  JSWUIElfl 


'Jandww  • 


I    «r  * 


•j^ndrqnii .  ;«, 


•x>l|dt)|n]\-  . 


•S  )SAU  JO  m3l!3-[ 


$    S 


I 

f 

2 


f    :   R    : 

n        •      ci        • 


•jandjlinw  • 


196 


STEAM  BOILERS. 


CHAP.  VIII. 


TABLE  XXVILz. 
FRENCH  PRACTICE  IN  SINGLE-RIVETED  JOINTS. 


From  D.  K.  Clark's  '  Manual  of  Rules.* 

1  hickness  of  plate. 

Diameter  of  rivet. 

Pitch  of  rivets. 

Lap. 

li 

Lj 
ri 

£•3  8 

i-IH 

'•sg-s 

li 

v      c 

C';3  o 
11- 

If 

— 

•fl  ®u 

0        c 

c--*13 

i 

J5 

^3        a! 

E      ° 
•5  o-g 

0        C 

rt  O        £ 

I'iPI 

i 

o  -s 

9 

ii 

o  •- 

SB'S 

A 

0     - 

o-s    •- 

3 

.118 

i- 

8 

•315 

A  + 

27 

1.  06 

irV  — 

3° 

1.18 

iA  — 

4 

.158 

10 

•394 

1     + 

32 

1.26 

ii  + 

34 

1-34 

rii  — 

5 

.197 

rV  ~4~ 

12 

.472 

li  "4" 

37 

1.46 

TrV  ~H 

40 

1.58 

i-j^-  -f- 

6 

.236 

li  4" 

14 

•551 

A— 

43 

1.69 

i^-|  -j- 

44 

i-73 

i  f  — 

7 

.276 

ft— 

16 

.630 

1  + 

48 

1.89 

i*  + 

5° 

1.97 

Ifi  ~t~ 

8 

•3'5 

fV  ~t~ 

17 

.669 

H- 

51 

2.OI 

2         + 

54 

2.13 

2  i  + 

9 

•354 

li  + 

19 

.748 

!- 

54 

2.13 

a*  + 

56 

2.  2O 

2T3T  ~t~ 

10 

•394 

1  + 

20 

.787 

1  + 

56 

2.  2O 

2t\  ~H 

58 

2.28 

2  i  ~t~ 

ii 

•433 

rV  — 

21 

.827 

tt  + 

57 

2.24 

2  i  — 

60 

2.36 

2  f    

12 

.472 

If  + 

22 

.866 

\  — 

58 

2.28 

2  i  ~H 

60 

2.36 

2  -|    

13 

•512 

i  + 

23 

.  .906 

I  + 

60 

2.36 

2  f  — 

62 

2.44 

2rV  "4~ 

14 

•55' 

rV- 

24 

•945 

62 

2.44 

2rV  + 

64 

2.52 

2i    + 

15 

•591 

H- 

25 

.984 

B+ 

63 

2.48 

2  i  — 

66 

2.60 

16 

.630 

1  + 

26 

1.024 

65 

2.56 

2A- 

68 

2.68 

2H  + 

LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


197 


TABLE    XXVIII. 
PROPORTIONS  OF  DOUBLE-RIVETED  LAP-JOINTS. 


Wilson. 

Fairbaim. 

Shipbuilding. 

Thickness 

Diameter  of 

Lloyd's  rule 

Liverpool  rule. 

Pitch. 

Lap. 

Lap.        Inches. 

Length. 

Lap. 

Lap. 

Butt-strap. 

Inch. 

Inches. 

Inches. 

Inches. 

Inches. 

A 

•Jo 

.. 

2.084     2 

i 

t  m 

.  . 

-L                >    —  ~ 

l& 

>             2.<;          - 

O 

-a 

.  . 

ft 

1 

i 
ft 

i 

"S;  s  ^  -j 

,_  5  i  = 

4 

H 
1 

diameter  of  ri 
\ii  from  edge. 

3-'34      g- 
3-333     "a 

....           CJ     — 

3-75   «•; 

<^-  .  —  > 

•  •  •  •         o    iO 

4-584     ^-£ 

he  thickness 
sheet. 

•S 

cn 
*•£  *C 

3 
3J 
3f 

4i 

4 

7i 
8 
8 

10 
10 
10} 

H        wjl"5       2| 

TS~              *  t»  t?  TJ            3l 

5J  ^ 

'  '  '  '         T3    4> 

.1 

1! 

cn 
cn 

si- 
si 
si 

3 

i            8-53.-        3i 

•£   rt 

6 

13 

_A             r-              -              } 
16             r"   ^  •_,  _±          3? 

>  " 

....         ^ 

^ 

O 

6I 

«3f 

i                   .S  -5  g    j     3i 

£ 

fc 

6J 

I4l 

198 


STEAM  BOILERS. 


CHAP.  VIII. 


16.  Various  Forms  of  Liap-joints. — On  account  of  the  inequality  of  stress  on 
the  transverse  and  longitudinal  joints  of  cylindrical  boilers  it  has  been  proposed  to 
arrange  the  joints  diagonally  (see  figure  64).  Taking  the  angle  of  the  joints  at  45°,  the 


Fig.  64. 


resultant  of  the  transverse  and  longitudinal  stresses 
per  inch  run  of  the  joint  is  found  by  calculation  to  be 
nearly  80  per  cent,  of  the  greater  stress,  acting  at  an 
angle  of  about  72°  to  the  joint. 

J.  G.  Wright  gives  the  strength  of  two  specimens 
of  single-riveted  square  lap-joints  and  two  of  diagonal 
joints,  at  an  angle  of  45°,  which  were  tested  by  Kirkaldy.  They  were  made  of  f-inch 
Staffordshire  plate,  exactly  .38"  thick,  12"  wide,  with  2J"  lap,  punched  holes,  and 
six  |f"  rivets  in  the  square  joint  at  2"  pitch.  The  diagonal  joint  was  made  with  eight 
rivets  of  the  same  size  and  pitch.  The  ultimate  tensile  strength  of  the  solid  plate  was 
19.69  tons  per  square  inch  with  the  fibre  and  16.80  tons  across.  The  sectional  area 
of  the  entire  plate  was  (12  X  .38)  —  4.56  square  inches.  The  net  sectional  area  of  the 
square  joint  was  2.71  square  inches,  and  the  shearing  section  of  the  rivets  3.11  square 
inches,  or  115  per  cent,  of  the  net  section. 


Ultimate  tensile  strength. 

Net  sectional  area. 

Net  tensile  strength  per  square 
inch  of  sectional  area  — 
per  cent. 

Tons. 

Per  cent. 

Square  inches. 

Per  cent. 

Entire  plate  

89.8 

43-° 
58.0 

IOO 
48 
64 

4-s6 
2.71 

3-98 

IOO 

59-4 
87.2 

IOO 
8l.2 

73-4 

Diagonal  joint  

It  will  be  seen  that  the  diagonal  joint  was  one-third  stronger  than  the  square  joint, 
although  per  square  inch  of  net  section  it  opposed  less  resistance. 

An  ingenious  method  of  increasing  the  strength  of  a  single-riveted  joint — that  of 
Webb — consists  in  having  the  rivets  of  oval  section,  and  placed  with  their  smaller  dia- 
meters in  a  straight  line  parallel  with  the  direction  of  the  seam,  and  the  transverse  dia- 
meters parallel  to  each  other  and  perpendicular  to  the  direction  of  the  seam,  as  in  figure 
65.  The  strength  of  this  joint  is  claimed  to  be  about  83  per  cent,  of  the  solid  sheet ; 
the  smaller  diameter  of  the  rivets  should  be  so  large  that  they  do  not  act  as  wedges  in 
splitting  the  sheet.  The  alleged  practical  difficulties  of  manufacture  disappear  when 
the  question  is  considered,  for  it  would  be  easy  to  punch  oval  holes  or  to  drill  them 
with  milling  tools  ;  the  rivets  also  could  be  made  in  oval  dies  as  well  as  in  circular  ones. 


SBC.  16. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


199 


Still  another  method  of  strengthening  a  joint  while  retaining  single-riveting  is  that 
of  Beattie,  who  has  patented  a  single-riveted  joint  over  which  is  a  covering-plate,  also 
single-riveted,  as  seen  in  figure  66. 

Fig.  66. 


Fig.  65. 


o 


o 


o    o    o    o 


o 


o 


When  it  is  difficult  to  set  a  sufficient  number  of  single-shear  rivets  a  forked  arrange- 
ment, like  that  in  figure  67,  may  be  employed,  making  the  riveting  double-shear  and  of 
half  the  number. 

A  method  of  double-riveting  which  would  greatly  increase  the  strength  of  the  joint, 

Fig.  67. 


Fig.  68. 


) 


Fig.  69. 


and  even  bring  it  to  equality  with  that  of  the  solid  plate,  has  been  proposed  :  it  is  to 
have  the  edges  of  the  plates  to  be  connected  rolled  thicker  than  the  rest  of  the  sheet, 


200  STEAM  BOILERS.  CHAP.  VIII. 

as  shown  in  figure  68,  and  Fairbairn  has  proposed  further  to  add  the  thickness  to  the 
faying  surfaces  and  to  plane  shoulders  on  each,  so  that  they  shall  lock  into  each  other 
— illustrated  by  figure  69.  By  these  means  the  strength  lost  in  the  holes  is  restored, 
but  the  difficulty  and  expense  of  manufacture  would  probably  prevent  their  general 
adoption. 

17.  Butt-joints. — The  proportions  of  a  single-welt  butt-joint  are  the  same  as  those 
of  a  lap-joint,  as  it  is  in  effect  equal  to  two  laps  in  juxtaposition ;  the  butt-strap  is 
made  equal  in  thickness  to  the  sheets  connected.  Although  single-welt  butt-joints  are 
not  stronger  than  lap-joints,  and  are  subject  to  the  same  distortion  on  account  of  the 
oblique  action  of  the  stress  on  the  rivets,  they  are  much  used  for  large  furnace-tubes 
subjected  to  an  external  pressure,  where  it  is  essential  to  preserve  a  perfectly  cylindrical 
form  ;  and  for  the  transverse  joints  of  cylindrical  shells,  which  experience  only  one-half 
the  stress  borne  by  the  longitudinal  joints,  and  where  a  tight  joint  is  more  easily  ob- 
tained with  a  single  welt  at  places  where  the  longitudinal  and  transverse  joints  meet ; 
and  in  the  flat  heads  of  cylindrical  boilers,  where  with  thick  plates  smoother  work 
can  be  made  with  butt-joints  than  with  lap-joints,  and  where  stiffness  is  of  greater  im- 
portance than  tensile  strength,  since  the  direction  of  the  principal  strain  is  at  right 
angles  to  the  plate.  The  joint  should  be  made  with  the  butt-strap  on  the  outside,  so 
that  it  is  accessible  for  subsequent  calking,  and  that  the  action  of  the  steam-pressure 
may  assist  in  preventing  the  opening  of  the  joint. 

In  the  double-welt  butt-joint  the  shearing  of  the  rivets  must  occur  in  two  places,  and 
on  this  account  their  resistance  is  very  nearly  twice  as  great  as  in  other  joints.  This 
joint  is  free  from  the  distortion  on  account  of  the  oblique  action  of  the  stress  on  the 
rivets  to  which  the  lap-joints  and  single-welt  butt-joints  are  subjected,  and  for  this  rea- 
son it  should  be  used  for  thick  plates  when  practicable.  Wilson  says  :  "Besides  the 
loss  of  strength  due  to  the  unequal  distribution  of  the  strain  through  the  whole  thick- 
ness of  the  plates  in  a  lap-joint,  very  thick  plates  are  also  liable  to  be  much  reduced  in 
strength  through  the  body  of  the  plate  by  injury  done  in  the  excessive  amount  of  set- 
ting they  require  where  the  transverse  and  longitudinal  seams  cross  each  other.  For 
this  reason  alone  butt-joints  should  always  be  used,  at  least  for  the  longitudinal  seams 
with  plates  over  £  inch  thick.  The  width  of  the  strap  for  double-riveting  should  be  at 
least  nine  times  the  diameter  of  the  rivet,  and  may  with  thick  plates  be  made  equal  to 
ten  times  the  diameter,  the  distance  from  the  centre  of  the  holes  to  the  edge  of  the 
plates  and  straps  in  all  cases  being  equal  to  the  diameter  of  the  rivet  multiplied  by  f." 

The  butt-straps  are  made  equal  in  thickness  to  at  least  one-half  the  thickness  of  the 
plates. 


SEC.  17.  LAYTNG-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  201 

Applying  the  same  notation  as  used  heretofore  the  proportions  of  the  double-welt 
butt-joints  are  found  from  the  following  equations : 

SiNGLE-KIVETED   DOUBLE-WELT  BUTT-JOINT. 

To  find  the  pitch  of  the  rivets. 

F=2nd?.  7854  S=n(p  —  d)tT; 

1.5708  tf  8  . 
P  =  --jT—  +  d; 

when  d  =  1.05 1  (see  section  13  of  the  present  chapter)  and  S  =  V  T; 

p  =  2.9  d. 

DOUBLE-RIVETED  DOUBLE- WELT  Buir-jcmr. 
To  find  the  pitch  of  the  rivets. 

F  =  4nd?  .7854  S=n(p  —  d)tT; 

3.1416  d*  S  . 
P  =  -~tT~    +  d; 

and  when  d  =  1.05 1  and  8  =  V  T; 
p  =  4.4  d. 

The  following  practice  prevails  at  the  Crewe  Works  (England),  where  Bessemer 
steel  is  used  for  locomotive  boilers  :  "The  joint  of  the  barrel  is  made  along  the  top, 
and  is  a  single-riveted  butt-joint,  with  inside  and  outside  covering-strips.  The  barrel- 
plate  is  Jf  inch  thick,  the  cover-strips  $  inch  thick  by  5J  inches  wide ;  rivets  J  inch 
diameter,  spaced  with  2  inches  pitch  and  placed  with  the  centres  about  1£  inches  from 
the  edge  of  the  plate.  This  joint  has  been  found  to  give  71.6  per  cent,  of  the  strength 
of  the  solid  plate.  The  rivets  are  of  steel.  A  noticeable  feature  in  the  proportioning  of 
the  joint  is  the  distance  of  the  rows  of  rivet-holes  from  the  edges  of  the  plate,  this  dis- 
tance having  been  found  necessary  to  prevent  the  distortion  of  the  holes  under  strain. 
On  the  other  hand,  in  the  cover-strips,  where  there  is  an  excess  of  strength,  the  holes 
come  at  an  ordinary  distance  from  the  edge,  so  that  there  is  no  difficulty  in  calking 
properly."  (Engineering,  October  15,  1879.) 

In  practice  it  is  convenient  to  have  all  the  holes  in  the  same  sheet  of  equal  size,  and 
to  use  as  small  a  variety  of  rivets  as  possible  in  the  same  boiler  ;  on  this  account  the 
diameters  of  rivets  as  found  by  the  above  formula  are  modified  to  suit  these  conditions. 
"The  greatest  difficulty  in  making  a  well-proportioned  joint  with  the  same-sized  rivets 
occurs  when  butt-joints  with  double  strips  and  lap-joints  come  together  in  the  same 
plate.  In  such  a  case  we  must  either  sacrifice  the  advantage  of  having  the  same-sized 


202 


STEAM  BOILERS. 


CHAP.  VIII. 


hole  throughout  the  plate  or  have  a  badly-proportioned  joint  in  one  seam  or  the  other. 
On  this  account,  when  double-fished  butt-joints  are  used  in  the  same  plate  with  lap- 
joints,  the  former  may  be  single  and  the  latter  double  riveted,  in  which  case  the  same 
pitch  and  diameter  of  rivet  might  be  judiciously  employed,  were  it  not  for  the  difficulty 
of  keeping  a  tight  joint  in  the  butt  arrangement,  which  necessitates  the  reduction  of  the 
pitch  unless  the  workmanship  is  very  good."  ( Wilson.) 

TABLE  XXIX. 

« 

WILSON'S  TABLE  OF  PROPORTIONS  OF  DOUBLE-RIVETED  BUTT-JOINTS  WITH  TWO  COVERING-PLATES. 


'o 

"3 

•o 

o 

•3 

•3 

•3 

KM 

o 

•3 

1 

V     . 

1 

I 

1 

V 

g 

1 

s  . 

is 

SI 

J  a 

j 

C  v 

II 

1 

1 

If 

£ 

S  S 
Jj3 

if 

•-  S 

j| 

15  ci« 

.2'C 

IS  tn 

B 

'Ja  o. 

• 

[J 

8 

2  o- 

rt  -j 

X   « 

ii 

H 

P 

H 

S 

H 

9 

H  " 

S 

H 

p 

H 

S 

Inch. 

Inch. 

Inch. 

Inches. 

Inch. 

Inch. 

Inch. 

Inches. 

Inch. 

Inch. 

Inch. 

Inches. 

1 

4 

J 

H 

I 

J 

4 

1 

3 

, 

I 

t 

3l 

TV 

4 

4 

H 

i 

j 
f 

1 

3i 

H 

I 

\ 

3! 

i 

i 

ft 

2j 

j 

i 

TV 

3i 

4 

A 

4 

rV 

tt 

A 

4 

ft 

* 

TV 

3i 

In  Kirkaldy's  experiments  on  the  comparative  strength  of  chain  and  zigzag  riveting 
in  double-welt  butt-joints,  summed  up  in  the  '  Eeport  of  the  Chief  Engineer  of  the 
Manchester  Boiler- Insurance  Company  for  1877,'  the  following  statement  occurs,  tabu- 
lated herewith,  showing  that  with  chain-riveting  greater  strength  is  obtainable  with 
smaller  pitch — a  great  advantage  in  calking  and  making  a  tight  joint.  It  will  also  be 
remarked  that  in  both  cases  thicker  plates,  larger  rivets,  greater  pitch,  and  drilled  holes 
gave  a  smaller  percentage  of  strength  compared  with  the  plate. 

TABLE  XXX. 


Number  of 
tests. 

Thickness  of 
plate. 

Diameter  of 

rivets. 

Pitch  of 
rivets. 

Rivet-holes. 

Ratio  of 
strength  of 
joint  to  plate. 

System 

of  riveting. 

Inch. 

Inch. 

Inches. 

Per  cent. 

2 
2 
2 
2 

TV 
TV 

4 

3 
3 

Punched  .... 
Punched  .... 
Drilled  

67.2 
66.9 
66.2 

63.3 

Chain. 
Zigzag. 
Chain. 
Zigzag. 

Drilled 

SEC.  17. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


203 


The  following  table  of  the  comparative  strength  of  punched  and  drilled  rivet- work, 
containing  the  result  of  Kirkaldy's  experiments,  is  taken  from  the  '  Proceedings  of  the 
Mechanical  Engineers  for  1872 '  and  forms  part  of  a  paper  read  by  W.  R.  Browne : 


TABLE  XXXI. 


Description  of  joint. 

Riveting.         Rivet-holes. 

Proportions. 

Ratio  of 
strength  of 
joint  to  that 
of  plate, 
per  cent. 

Diameter  of 
rivets  to 
thickness  of 
plates. 

Lap  or  cover  to  diameter 
of  rivets. 

Pitch  to 

diameter  of 
rivets. 

Lap. 

Lap  

c,.     ,      (  Punched.  . 
Smgle.  |   Drilled... 

2 
2 

3 

3 

3 
4 

55 
62     . 

Chain. 

Zigzag. 

„     ,  .    (   Punched.  . 
Double]  Drilled... 

2 
2 

5i 

5 

6 
Si 

4* 

4 

69 
75 

Covering-  strip. 

Butt,  i  cover.  .  . 

~-     ,      (   Punched.  . 
Single.  -J  Drilled... 

2 
2 

6 
6 

k 

55 
62 

Chain. 

Zigzag. 

Butt,  i  cover.  .  . 

T-.     ,  ,     (   Punched.  . 
Double]   Drilled_ 

2 

2 

ii 
10 

12 
11 

4i 

4 

69 

75 

Butt,  2  covers.  . 

„.     ,       (   Punched.. 
Smgle.  j   orined... 

1} 
I* 

6 
6 

3i 
3 

57 
67 

Chain. 

Zigzag. 

Butt,  2  covers  .  . 

„     ,  ,     (   Punched.  . 
Double  -j   Drilled... 

1^ 
Ii 

ii 

10 

»3 

12 

5f 

4f 

72 
79 

The  experiments  recorded  in  the  following  table  have  been  selected  from  the  '  First 
Report  of  the  Committee  of  the  Institute  of  Mechanical  Engineers  on  the  Form  of 
Riveted  Joints.'  The  stresses  corresponding  to  the  actual  mode  of  fracture  are  printed 
in  heavy  type  ;  the  other  stresses,  printed  in  ordinary  type,  are  those  which  obtained  at 
the  moment  of  fracture,  but  are  lower  than  those  at  which  the  joint  would  have  given 
way  by  the  respective  modes  of  fracture.  The  joints  marked  d,  e,  and  /  in  the  table, 
and  their  lines  of  fracture,  are  represented  in  figures  70,  71,  and  72  respectively.  The 
steel  plates  had  a  nominal  thickness  of  f  inch.  The  butt-straps  were  T9F  inch  thick,  and 
the  steel  rivets  had  a  diameter  of  1.13  inches.  The  tensile  strength  of  the  rivets  was 


204 


STEAM  BOILERS. 


CHAP.  VIII. 


28.9  tons  per  square  inch,  and  the  apparent  shearing  strength  of  the  rivets  in  experi- 


Fig.  70. 


Fig.  71 


> 

r 

)- 


\( 

-eH-*-e-f--e>- 

<a 

— 

zjujj^r. 

i./l  _ 

k- 

in         •- 

> 


> 


ment/was,  therefore,  68.5  per  cent,  of  their  tenacity.     In  experiments  d  and  e  the 
plates  broke  on  the  line  marked  in  figures  70  and  71. 

TABLE    XXXII. 

RESULTS  OF  EXPERIMENTS  WITH  SINGLE  AND  DOUBLE-RIVETED  DOUBLE-WELT  BUTT-JOINTS. 


. 

.E 

Stress  at  moment  of  frac- 

li 

I 

U 

0)  J= 

ture  in  tons  per  sq.  in. 

—  i  rt 

.- 

n  e 

•*"  S 

*-' 

• 

"^'S 

O  w 

;| 

Mode  of  riveting. 

Holes. 

I 
O 

i! 

rt  .;  " 

I  si 

•s 

Remarks. 

• 

"E, 

a 

•S  a 

JU 

ttt 

3 

iS 

X 

u 

gj 

•a 

8 

J 

i 

rt       w 

giS'S 

ji 

M 

H 

H 

M 

u 

H 

Single-riveted  

Punched  

Iron      plates 
and  rivets. 

25-77 

24.31 

16.38 

43-09 

94 

H 

iMean  of  three  experi- 
ments by  Fairbairn. 

u               

Drilled  

22.25 

24.24 

11.48 

33-83 

109 

63 

Greig  and  Eyth. 

^ 

H 

Steel     plates 

36.22 

36.62 

18.75 

52.04 

ZOI 

60 

Henry  Sharp. 

Double-riveted  

Punched  

and  rivets. 
Iron      plates 
and  rivets. 

2S-77 

21.44 

10.82 

25.17 

83 

Mean    of  two    experi- 
ments by  Fairbairn. 

** 

Drilled    

22.25 

20.65 

8.92 

25.72 

93 

64 

Greig  and  Eyth. 

i 

Plates    i    inch     thick. 

"                

Punched  

H 

'9-35 

17.52 

6.90 

13.00 

91 

j 

Two  experiments,  R. 

54  1 

V.  J.  Knight. 

H 

Drilled            .  .     . 

Steel     plates 
and  rivets. 

36.22 

42.93 

13.16 

37.20 

"9 

70 

Henry  Sharp. 

U 

Punched    . 

u 

36.22 

39.11 

11.57 

33.56 

108 

63  i 

Mean   of    ten     experi- 

H 

K 

u 

36.20 

33.75 

15.30 

41  -'39 

93 

64  < 

ments.       Plates    an- 

nealed.    D.  Kirkaldy. 

Double-riveted  (zigzag)  (d)  . 

Drilled  and  reamed. 

H 

28.10 

20.O4 

16.40 

21.92 

71 

59  " 

(«). 

Punched  and  ream'd 

it 

27.10 

22.73 

16.80 

22.66 

84 

63 

David  Kirkaldy.  Plates 
%  inch  thick. 

Double-riveted  (chain)  (f).. 

Drilled  and  reamed. 

H 

28.20 

27.23 

16.80 

27.10 

73  . 

18.  Calking. — Since  the  surfaces  of  boiler-plates  are  always  more  or  less  rough,  the 
riveted  joints  require  calking  to  make  them  steam  and  water  tight.  Calking  consists  in 
bringing  the  extreme  edge  of  one  boiler-plate  so  close  to  the  solid  part  of  the  other  that 
there  shall  be  no  leakage  between  the  two.  Calking  should  always  be  done  on  both 


SBC.  18. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


205 


Fig.  73. 


sides,  where  it  is  possible  to  do  so.  If  the  riveting  has  not  entirely  closed  the  extreme 
edge  a  heavy  hammer  has  to  be  used  to  do  this.  Wedges  or  pieces 
of  hoop-iron  should  never  be  driven  between  the  hips,  nor  should 
sal-ammoniac  or  any  other  substance  be  used  to  make  the  joint  tight 
by  rusting.  If  the  edge  of  the  plate  has  not  already  been  planed  it 
should  be  chipped  smooth  to  an  angle  of  about  110°.  The  tools  or- 
dinarily in  use  are  represented  in  figure  73. 

The  bevel  of  the  calking-tool  should  be  about  20°,  the  sharp 
corner  being  first  used  for  making  a  slight  indentation  in  the  lap- 
edge — this  operation  is  called  splitting  the  lap;  then  the  tool  is 
turned  and  the  whole  width  is  used  for  driving  in  or  upsetting  the 


Fig.  74 


edge  against  the  sheet.  Care  must  be  taken  not  to  move  the  calking-tool  its  entire 
breadth  after  each  blow,  else  small  places  will  be  left  uncalked  ;  one  hard  blow  at  each 
place  should  be  sufficient.  Sexton  says  that  the  proper  thickness  for  a  calking-tool  for 
plates  from  f  inch  to  $  inch  thick  is  ^  inch  ;  for  plates  more  than  £  inch  thick  the  tool 
should  be  i  inch. 

Cannery's  calking-tool  is  made  convex,  so  that  it  shall  not  cut  the  metal.  The  com- 
parative working  of  the  two  tools  is  shown 
in  the  sketch  (figure  74),  which,  however, 
is  somewhat  exaggerated  ;  the  old  method, 
shown  to  the  right,  is  to  chip  or  plane  the 
edge  of  the  lap,  then  to  drive  up  the  tool, 
indenting  the  lower  sheet  and  tending  to  curve  the  lap  upward  as  shown  in  dots  ;  if 
afterward  the  lower  sheet  be  bent,  either  purposely  or  by  the  action  of  unequal  expan- 
sion, grooving  ensues  at  the  indentation  caused  by  the  tool.  With  the  concave  tool 
a  depression  is  made  in  the  edge  of  the  lap,  and  the  lower  portion  of  the  lap  is  driven 
against  the  other  sheet  without  injuring  the  latter  ;  the  comparative  extent  of  compres- 
sion in  the  two  methods  is  said  to  be  shown  by  the -wedge  of  dark  shading  in  the  two 
cases. 

The  butt  is  calked  with  the  tool  delineated  in  figure  75,  which  makes  an  indentation 
as  sketched  at  figure  76. 

Boilers  should  not  be  calked  under  pressure,  as  the  jarring  would  probably  start 
leaks  in  seams  elsewhere.  Excessive  calking  of  lap-joints  works  mischief  in  several 
ways  :  thin  plates  may  be  forced  apart  when  a  set  and  heavy  hammer  are  used — this  is 
shown  in  figure  57 ;  when  the  edge  of  the  calking-tool  is  very  thin  it  sometimes  acts  as 
a  wedge,  forcing  the  joint  wide  open.  In  contrast  with  the  foregoing,  figure  77  is  given 


200 


STEAM  BOILERS. 


CHAP.  VIII. 


from  Burgh's  'Practical  Treatise,'  which  he  calls  "an  illustration  of  the  result  of  pro- 
per drilling,  fitting,  riveting,  and  calking." 

Fig.  75.  Fig.  77. 


Fig.  76. 


19.  Welding. — Nasmyth  says  of  welding  that  it  consists  in  inducing  upon  malle- 
able iron,  by  means  of  a  very  high  heat,  a  certain  degree  of  adhesion,  so  that  any  two 
pieces  of  malleable  iron,  when  heated  to  the  requisite  degree,  will,  if  brought  into  close 
contact,  adhere  or  stick  together  with  a  greater  or  less  tenacity,  according  to  the 
amount  of  force  applied  to  urge  them  into  close  contact.  .  .  .  The  chief  cause  of 
defective  welding  arises  from  portions  of  the  vitreous  oxide  of  the  iron  being  shut  up 
between  the  surfaces  at  the  part  presumed  to  have  been  welded  ;  and  since,  besides  the 
impossibility  of  ascertaining  in  the  majority  of  cases,  after  the  process  of  welding  has 
been  gone  through,  whether  or  not  this  vitreous  oxide  has  been  thoroughly  expelled 
and  the  surfaces  at  the  welding  brought  into  perfect  metallic  union,  no  after-heating 
or  hammering  can  dislodge  the  vitreous  oxide  when  once  it  has  effected  a  lodgment,  our 
best  and  only  true  security  is  to  form  the  surfaces  of  the  iron,  at  the  part  where  the 
welding  is  desired  to  take  place,  so  that  when  applied  to  each  other  when  at  the  weld- 
ing-heat their  first  contact  with  each  other  shall  be  in  the  centre  of  each. 

Much  attention  has  been  paid  of  late  to  the  effect  of  chemical  composition  on  the 
welding  of  iron.  D.  Adamson  states  in  his  paper  read  before  the  Iron  and  Steel  In- 
stitute, September,  1878 :  "After  many  trials  and  many  failures  in  attempting  to  weld 
steel  boiler-plates  the  writer  found  it  necessary  to  ascertain  in  all  cases  the  composition 
of  the  metal  before  putting  any  labor  upon  it,  and  from  a  large  experience  it  is  now 
considered  desirable  that  the  carbon  should  not  exceed  0.125  per  cent.,  while  the  sul- 
phur and  phosphorus  should,  if  possible,  be  kept  as  low  as  0.04  per  cent.,  silicon  being 
admissible  up  to  the  extent  of  0.1  per  cent." 

A.  L.  Holley,  in  a  paper  read  before  the  American  Institute  of  Mining  Engineers 
in  February,  1878,  discusses  the  results  obtained  by  the  United  States  Test-Board  in 
experiments  upon  fourteen  brands  of  wrought-iron  intended  for  chain-cables.  He  comes 


SBC.  20.  LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC.  207 

to  the  following  conclusions,  viz.  :  "Phosphorus  up  to  the  limit  of  one-quarter  per 
cent,  had  not  a  notable  effect  on  welding."  "  Carbon  notably  affected  welding.  It 
ran  in  connection  with  regularly  decreasing  welding  power  from  0.02  to  0.35  per  cent." 
"Carbon,  in  a  greater  degree  than  phosphorus,  promotes  fluidity;  hence  the  iron  is 
burned  at  the  ordinary  welding  temperature  of  low-carbon  irons."  "  Slag  should  theo- 
retically improve  welding,  like  any  flux,  but  its  effects  in  these  experiments  could  not 
be  definitely  traced."  "  The  experiments  prove  that  the  strength  of  the  link,  which  is 
chiefly  dependent  on  welding  power,  as  compared  with  the  bar  was  more  decreased  by 
overworking  (in  reducing  the  pile  to  the  bar)  than  by  any  other  cause,  excepting  the 
high  carbon  in  the  steely  iron  L  and  the  excessive  copper,  phosphorus,  etc.,  in  the 
peculiar  iron  M."  Regarding  the  strength  of  the  welded  joint  of  the  latter  iron  he 
says :  "Its  surfaces  were  pretty  well  united  by  welding,  but  the  iron  about  the  weld 
was  weakened,  especially  at  a  high  heat.  Of  59  ruptures  of  links  made  of  this  iron,  33 
were  through  the  weld  and  the  iron  was  little  distorted.  Of  303  ruptures  of  links  made 
of  other  irons,  but  36  were  through  the  weld." 

He  proposes  the  following  theory  regarding  welding:  "  It  is  certain  that  perfect 
welds  are  made  by  means  of  perfect  contact  due  to  fusion,  and  that  nearly  perfect  welds 
are  made  by  means  of  such  contacts  as  may  be  got  by  partial  fusion  in  a  non-oxidizing 
atmosphere  or  by  mechanical  fitting  of  the  surfaces,  whatever  the  composition  of  the 
iron  may  be  within  all  known  limits.  While  high  temperature  is  thus  the  first  cause 
of  that  mobility  which  promotes  welding,  it  is  also  the  cause,  in  an  oxidizing  atmos- 
phere, of  that  'burning'  which  injures  both  the  weld  and  the  iron.  Hence  welding 
in  an  oxidizing  atmosphere  must  be  done  at  a  heat  which  gives  a  compromise  between 
imperfect  contact  due  to  want  of  mobility  on  the  one  hand  and  imperfect  contact  due  to 
oxidation  on  the  other  hand.  This  heat  varies  with  each  different  composition  of  irons. 
It  varies  because  these  compositions  change  the  fusing-points  of  irons,  and  hence  their 
points  of  excessive  oxidation.  Hence,  while  ingredients  such  as  carbon,  phosphorus, 
copper,  etc.,  positively  do  not  prevent  welding  under  fusion  or  in  a  non-oxidizing  at- 
mosphere, it  is  probable  that  they  impair  it  in  an  oxidizing  atmosphere,  not  directly  but 
only  by  changing  the  susceptibility  of  the  iron  to  oxidation. 

"The  obvious  conclusions  are:  1st.  That  any  wrought-iron,  of  whatever  ordinary 
composition,  may  be  welded  to  itself  in  an  oxidizing  atmosphere  at  a  certain  tempera- 
ture, which  may  differ  very  largely  from  that  one  which  is  vaguely  known  as  '  a  weld- 
ing-heat.' 2d.  That  in  a  non-oxidizing  atmosphere  heterogeneous  irons,  however  im- 
pure, may  be  soundly  welded  at  indefinitely  high  temperatures." 

2O.  Welding  Boiler-plates. — The  welding  of  boiler-plates  was  first  successfully 


208 


STEAM  BOILERS. 


CHAP.  VIII. 


Fig.  78. 


tried  by  W.  Bertram,  at  Woolwich  Dockyard,  in  1857.     His  method  is  represented  in 

figure  78.  The  edges  of  the  plates  are 
scarfed  and  placed  together ;  two  non- 
oxidizing  gas-flames  are  obtained  by  the 
combustion  of  coal  or  coke  in  suitable 
furnaces,  and  these  are  directed  against 
either  side  of  the  plates  until  they  are 
raised  to  a  welding-heat,  when  they  are 
united  by  pressure  or  hammering.  For 
this  purpose  a  number  of  stampers  are 
sometimes  used  —  viz.,  upright  rams 
raised  by  four- toothed  cams  and  falling  by  their  weight  upon  the  work,  which  is  placed 
on  an  anvil.  The  work  is  said  to  be  done  three  or  four  times  as  expeditiously  as  hand- 
riveting. 

The  scarf -weld,  either  of  the  form  shown  in  figure  78  or  else  prepared  as  drawn  in 
figure  79,  is  much  stronger  than  the  lap-welded  joint,  which  is  shown  in  figure  80,  since 

Fig.  81. 
Fig.  79. 


Fig.  80. 


i / 


the  strain  on  the  scarfed  joint  is  direct,  instead  of  tending  to  spring  the  joint  ^as  with 
the  lap- welded  plates  shown  in  figure  81.  The  lap-weld  should  be  used,  on  this  account, 
only  with  very  thin  plates.  The  welded  joints  of  thicker  plates  might  be  greatly  in- 
creased in  strength  by  a  covering- plate,  as  shown  in  figure  82. 

The  seams  of  the  flues  of  high-pressure  boilers  are  frequently  welded  in  the  manner 

Fig.  83.  Fig.  84. 


Fig.  82. 


illustrated  in  figure  83.  The  edges  of  the  bent  sheet  are  kept  apart,  a  distance  of  about 
&  inch,  by  small  blocks,  a  a,  the  sheet  being  held  together  by  the  bands  b  5,  secured  by 
bolts  and  nuts.  A  narrow  strip,  c  c,  is  welded  over  the  seam  to  the  plates  at  each  end, 
in  order  to  hold  them  more  securely  in  position.  The  two  edges  and  a  rod  of  a  wedge- 
shaped  or  round  section  are  brought  to  a  welding-heat  in  an  open  fire ;  the  tube  is 
passed  over  the  long  horn  of  an  anvil,  the  rod  is  inserted  between  the  edges,  and  all 


SBC.  20. 


LAYING-OFF,  FLANGING,  K1VETING,  WELDING,  ETC. 


209 


three  parts  are  welded  by  hammering  for  a  distance  of  a  few  inches.  Then  the  nearest 
band  and  block  are  moved  along,  the  rod  is  cut,  another  heat  is  taken,  and  the  process 
is  repeated.  In  small  tubes  where  pressure  by  machinery  can  be  applied  the  weld  can 
be  made  with  a  butt-joint. 

The  following  practical  points  in  reference  to  welding  are  selected  from  Sexton's 
'  Boiler-makers'  Pocket-book.'  Pipes  or  cylinders  up  to  four  feet  diameter  may  be 
easily  welded  in  the  following  manner :  Bend  the  pipe  or  cylinder  in  the  form  of  figure 
84,  the  edges  A  and  B  not  touching  by  about  a  quarter  of  an  inch  ;  place  it  on  a  clear 
fire,  throw  a  little  sand  and  scale  on  the  edges,  turned  downward ;  place  a  fire-brick  on 
the  part  through  which  the  greatest  heat  is  coming.  The  brick  is  a  very  slow  conductor 
of  heat,  and  will  greatly  assist  the  iron  in  getting  hot,  as  it  does  not  absorb  much  heat 
itself.  The  blast  is  started  moderately  till  the  iron  becomes  of  a  pale  yellow,  then  put 
on  strongly  till  the  iron  is  white-hot,  when  the  work  is  brought  out  and  placed  on  the 
mandrel  as  quickly  as  possible.  The  first  blow  should  fall  gently  on  the  edge  A,  and 
B  is  hammered  down  on  it ;  and  when  the  iron  has  cooled  so  as  not  to  fly  to  pieces 
under  the  blows  these  are  repeated  as  hard  and  quickly  as  possible  until  the  edge  has 
disappeared  and  a  smooth  surface  is  left.  There  is  also  an  arrangement  of  a  forge  on 
wheels  made  to  run  inside  the  cylinder  with  an  india-rubber  blast-pipe  connected  to  it, 
and  when  the  lap  of  the  plate  is  sufficiently  heated  Fig.  85. 

the  forge  is  withdrawn  and  an  anvil  wheeled  in  its 
place. 

In  welding  the  longitudinal  seams  of  a  boiler 
one  inch  thick,  with  four  plates  to  the  circle,  the 
plates  are  punched  for  the  circumferential  seams, 
but  not  quite  to  the  longitudinal  edges  ;  these  last 
are  then  planed  to  an  angle  of  45°  ;  then,  after 
being  rolled  and  set,  the  plates  are  fastened  to- 
gether temporarily  with  the  planed  edges  inside. 
These  edges  are  heated  in  a  clear  fire  at  the  same 
time  that  a  piece  of  square  iron  is  heated  in 
a  separate  fire,  and,  when  sufficiently  heated,  the 
boiler,  suspended  from  a  suitable  crane,  is  brought 
out,  placed  on  the  block,  the  square  iron,  which 
is  rather  hotter  than  the  plates,  laid  in  cornerwise,  as  at  C  in  figure  85,  and  hammered 
direct  on  the  upper  corner.  Six  or  seven  inches  at  a  heat  will  be  sufficient  to  weld. 
The  weight  of  the  ring  of  plates  must  not  rest  on  the  block,  or  it  will  become  flat. 


210 


STEAM  BOILERS. 


CHAP.  VIII. 


The  bar  should  have  its  sides  equal  in  width  to  the  planed  edge  of  the  plate.  The 
welding  should  be  commenced  in  the  middle  and  worked  towards  the  ends,  which  are 
kept  securely  bolted  as  long  as  is  necessary.  In  putting  the  rings  together  the  welded 
seams  should  break  joint.  In  furnace-tubes  the  weld  should  be  below  the  grate. 

When  it  is  desirable  to  have  the  front  of  a  boiler  in  one  piece  but  a  plate  of  suffi- 
cient size  cannot  be  procured,  two  plates  may  be  welded  together,  either  by  laying  in  a 
square  bar,  as  in  figure  86,  or  by  thickening  both  edges,  splitting  one  and  tapering  the 


Fig.  86. 


Fig.  87. 


Fig.  88. 


f~ 


other,  as  sketched  in  figure  87,  then  forcing  one  into  the  other,  as  shown  in  figure  88 ; 
this  form,  however,  is  not  favorable  for  the  escape  of  the  scale,  and  the  difference  in 
thickness  of  the  edges  in  the  fire  is  not  favorable  for  the  iron  being  properly  and  uni- 
formly heated.  It  is  more  applicable  for  welding  bars  and  plates  of  very  short  length. 
The  plates  are  secured  by  several  short  pieces  of  angle-iron  bolted  to  them,  and  by  as 
many  turn-buckles  and  chains  as  the  length  of  the  work  requires  (see  figure  89),  then 
placed  in  the  fire  so  as  to  heat  the  edges  in  question.  When  the  plate  is  hot  the  ex- 
pansion of  the  metal  acting  against  the  strain  of  the  screws  will  weld  the  plates  even 
before  they  are  hammered  on  the  block,  which,  of  course,  must  be  done  when  suffi- 
ciently heated. 

Fig.  90.  Fig.  91. 

Fig.  89. 


"  In  welding  angle-iron  rings  for  flanging,  for  strengthening  flues,  etc.,  the  ends  are 
upset  and  scarfed  or  bevelled  on  the  side  required  ;  then,  a  short  heat  being  taken,  about 
six  inches  at  each  end  are  bent ;  next,  as  long  a  heat  as  possible  being  got,  the  ring  is 
bent  around  a  shaper  to  the  required  curve.  The  ends  of  an  external  ring  shoiild  have 
the  lump  inside  before  welding,  as  in  figure  90,  since  this  ring  must  be  hammered  on 
the  inside  during  the  welding  process  ;  while  in  the  internal  ring,  figure  91,  the  lump  is 
left  on  the  outside,  that  being  the  side  on  which  the  ring  is  most  hammered. 

"In  making  up  a  fire  for  welding,  as  the  article  in  question  is  not  to  be  made  hot  all 


SEC.  21. 


LAYING-OFF,  FLAGGING,  RIVETING,  WELDING,  ETC. 


211 


over,  but  only  at  the  part  to  be  welded,  the  size  of  the  fire  should  be  limited  to  that 
portion.  For  complicated  shapes  the  small  coal  may  be  wet  and  built  up  around  the 
object  or  a  rude  pattern  of  it,  and,  the  latter  being  withdrawn,  the  hole  filled  with  clean 
hot  coke,  together  with  small  fresh  coke  ;  next,  the  object  being  put  in  position,  some 
sand  is  sprinkled  on  the  edges  to  be  welded,  which  are  then  covered  with  a  fire-brick, 
the  blast  is  started  gently,  and  wet  coal  built  up  around  what  soon  becomes  a  hollow 
fire  ;  this  should  be  disturbed  as  little  as  possible,  and  only  to  watch  its  progress.  The 
blast  is  presently  increased,  and  when  the  sand  is  melted,  and  the  metal  white  and  be- 
ginning to  emit  brilliant  white  sparks,  the  work  may  be  brought  out,  and  no  time  must 
then  be  lost  in  the  welding,  all  tools  being  in  place  and  preparations  made  beforehand." 

One  of  the  advocates  of  welding  says  :  "  Among  the  difficulties  of  welding  plates  are 
that  they  heat  unequally,  buckle,  blister,  and  frequently  become  exposed  while  hot  to 
the  air  for  a  space  of  time  sufficient  to  provide  a  coat  of  oxide  fatal  to  the  future  joint. 
But  by  the  adoption  of  this  principle  we  could  reduce  the  thickness  of  boiler-plates  by 
one-half,  rendering  them  lighter  and  more  easily  worked  and  handled  in  every  way. 
The  expense  incurred  should  not  be  higher  than  that  of  the  riveted  joint ;  the  extra 
trouble  of  fitting  and  scarfing  would  not  equal  that  of  punching,  and  the  fuel  consumed 
in  rivet  making  and  heating  would  nearly  suffice  for  welding.  There  are  certain  situa- 
tions in  a  boiler  where  this  process  would  be  inapplicable  and  where  rivets  would  have 
to  be  used.  In  early  experiments  a  seam  12  feet  long  in  f-inch  plates  was  welded  in 
one  hour  and  twenty  minutes  with  mouth-pieces  or  nozzles  only  6  inches  long." 

21.  Strength  of  Welded  Plates. — Wilson  gives  the  result  of  some  experiments 
recorded  by  Kirtley  on  the  tensile  strength  of  strips  cut  across  the  weld  and  taken  from 
several  boilers  with  welded  longitudinal  seams ;  the  strips  were  7£  inches  long  and 
-fa  inch  thick : 


Width  of  strip. 

Number  of 
strips  tested. 

Broke  in 
weld. 

Broke    in 

solid. 

Breaking  strength  in  tons  per  square  inch. 

Inch. 

Least. 

Greatest. 

Mean. 

I 

I.I 

4 

IS 

4 
4 

8 
2 
I 

7 

2 

3 

16.5 
19.6 

18.1 

23.8 
22.2 

23-5 

20.2 
21.0 
21.7 

Total  

23 

II 

12 

16.5 

23.8 

2O.6 

1  1  strips  of  the  same  plates  unwek 

led  

20.7 

25-8 

23.6 

After  giving  the  foregoing  table  he  proceeds:  "It  appears  from  these  results  that 


212  STEAM  BOILERS.  CHAP.  VIH. 

half  of  the  test-pieces  broke  in  the  solid,  and  not  at  the  weld.  The  average  loss  of 
strength  of  the  23  welded  plates  was  only  12.7  per  cent,  compared  with  the  strength  of 
the  11  unwelded  plates  ;  the  worst  pieces,  showing  as  defective  a  weld  as  would  occur  in 
practice,  had  70  per  cent,  of  the  average  strength  of  the  unwelded  plates.  The  weld  is 
best  made  when  the  edges  of  the  plates  are  upset  at  a  red-heat,  by  hammering  or  pres- 
sure, to  nearly  double  their  thickness,  and  bevelled  to  an  angle  of  about  45°.  The 
edges  can  then  be  heated  simultaneously,  and  the  weld  made  by  hammering  down  the 
joint  to  the  original  thickness  of  the  plate.  In  some  cases  it  has  been  found  that  the 
plates  are  rapidly  pitted  at  the  weld."  This  is  doubtless  owing  to  the  outer  protecting 
film  or  skin  being  removed  by  the  fire  and  working. 

"  Some  time  ago  Mr.  Gillott,  of  Farnley,  who  has  had  great  experience  in  smithing 
boiler-plates,  had  reason  to  suspect  that  in  welding  boiler-tubes  in  successive  heats  and 
in  short  lengths  after  the  ordinary  manner  there  is  a  straining  action  upon  the  length 
already  welded,  owing  to  the  expansion  under  heat  of  the  adjacent  length  being 
welded,  and  we  are  indebted  to  Mr.  Gillott  for  the  following  results  of  some  experi- 
ments he  made.  In  order  to  ascertain  the  correctness  of  his  views  he  took  a  welded 
and  flanged  tube  2  feet  8  inches  in  diameter,  3  feet  long,  of  T\-inch  best  Yorkshire  plate, 
welded  by  hand-hammers,  ahd  in  every  respect  a  fair  average  job.  The  plate  was 
prepared  for  welding  with  a  "bent  scarf,"  so  that  the  finished  work  was  generally  some- 
what thicker,  or  at  any  rate  not  less,  than  the  solid  plate.  The  welding  was  commenced 
at  the  middle  of  the  plate  and  worked  towards  each  end.  The  tube  was  put  in  a  lathe, 
and  a  length  of  about  5  inches  was  cut  off  one  end.  Six  rings  were  then  cut  off  about  2 
inches  wide  and  numbered  consecutively  1  to  6,  counting  from  the  edge  where  the 
5-inch  length  was  cut  off,  so  that  the  piece  marked  6  would  be  about  the  original  middle 
of  the  plate.  Strips  2  feet  6  inches  long,  having  the  weld  approximately  in  the  centre, 
were  cut  from  each  ring,  and  similar  strips  of  the  solid  plate  also.  The  strips  were  then 
all  heated  and  carefully  straightened."  .  .  .  "  The  strips  were  then  tested  by  being 
pulled  asunder,  with  the  results  given  in  the  annexed  table."  .  .  .  "Not  only  the 
strength  but  the  ductility  of  the  weld  diminished  progressively  from  the  end  to  the 
middle  portion  of  the  plate,  or  from  the  part  last  welded  to  that  which  was  first  welded." 
All  strips  broke  at  the  weld. 

"In  a  furnace-tube,  where  the  pressure  tends  to  assist  in  keeping  the  weld  together, 
the  limited  tensile  strength  due  to  the  unsoundness  of  the  weld  may  be  outweighed  by 
other  advantages,  as  for  flanging,  etc.,  which  the  welding  gives  ;  but  for  the  longitudinal 
seams  of  boiler-shells  the  uncertainty  of  making  a  sound  and  strong  weld,  when  the 
job  is  done  in  lengths,  renders  it  difficult  to  conclude  otherwise  than  that  such  welding 


SEC.  21. 


LAYING-OFF,  FLANGING,  RIVETING,  WELDING,  ETC. 


213 


is  not  so  good  as  riveting,  notwithstanding  the  liability  of  the  latter  to  leak.  This  con- 
clusion does  not  apply  to  joints  where  the  weld  is  completed  at  one  heat  by  pressure 
either  with  rolls  or  otherwise."  (Engineering,  January  31,  1879.) 


Mark. 

* 

w. 

w, 

w. 

w. 

w. 

Average  result  for 
strips  of 
solid  plate. 

Breaking  weight,  in  tons  per 
sq.  in  of  original  area.  

2*2.4. 
*-?* 

IQ  J.8 

18  7? 

17.67 

16  3 

Elongation  per  cent,  in  18 
inches. 

o~_>*  u  ei 
g^"2-«'S. 

9-375 

6-597 

6.25 

4.166 

3-472 

23-34 
17.71 

OF    THE 

UNIVERSITY 

Of 


CHAPTER  IX. 


SHELL,    FURNACES,    AND  BACK-CONNECTIONS. 

1.  Various  Forms  of  Shells. — The  forms  commonly  given  to  the  shell  of  marine 
boilers  have  been  described  and  illustrated  in  section  3,  chapter  vii.  These  forms  are 
produced  by  combining  flat  and  cylindrical  plates  in  various  ways.  Figure  92  illus- 
trates one  form  of  the  "  connected-arc  Fig.  92i 
marine  boiler"  of  C.  E.  Emery,  who 
states  that  "  the  object  of  the  invention 
is  to  construct  steam  boilers  of  great 
strength,  with  the  minimum  amount  of 
small  stays  or  braces,  and  in  such  form 
as  to  occupy  less  room  for  a  given  power 
than  ordinary  cylindrical  boilers ;  also 
to  obtain,  when  desirable,  a  large  boiler 
of  moderate  height." 

When  such  a  boiler  is  braced  according  to  the  rules  given  in  section  7,  chapter  vi., 
the  plates  forming  the  several  arcs  experience  only  a  tensile  strain,  like  the  circular  shell 
of  a  cylindrical  boiler,  while  the  flat  surfaces  of  boilers  are  subjected  to  bending  strains. 

The  thickness  of  the  plates  forming  the  cylindrical  portions  of  the  shell  is  found  by 
formula  [III.],  section  2,  chapter  vi.,  by  making  the  value  of  7c  equal  to  the  ultimate 
strength  of  the  joints  divided  by  a  factor  of  safety  ;  the  strengths  of  various  joints  rela- 
tively to  the  strength  of  the  entire  plate,  as  determined  by  experiment,  are  given  in 
sections  15  and  17,  chapter  viii. 

The  strength  of  the  flat  surfaces  of  the  shell  of  boilers  depends  almost  entirely  on 
the  bracing  and  staying,  the  plates  being  made  thick  enough  to  give  them  proper  stiff- 
ness. Plates  less  than  one-quarter  inch  thick  cannot  be  calked  efficiently,  and  are 
therefore  not  used  for  boiler-shells.  Tight  joints  cannot  well  be  made  by  riveting 
together  plates  varying  greatly  in  thickness ;  on  this  account  the  thickness  of  the 
flat  plates  of  the  shell  does  not  vary  generally  more  than  one-eighth  inch  from  that  of 
the  cylindrical  plates.  Various  methods  of,  and  rules  for,  staying  the  flat  surfaces  of 
boilers  will  be  found  in  chapter  x. 

In  places  where  holes  are  cut  in  the  shell  for  handholes,  manholes,  etc.,  stiff ening- 

214 


SBC.  2.  SHELL,  FURNACES,  AND  BACK-CONNECTIONS.  215 

plates  or  angle-irons  are  riveted  around  the  opening.  In  cylindrical  shells,  depending 
on  their  form  for  strength,  it  is  important  that  these  compensating-rings  do  not  only 
stiffen  the  weakened  parts,  but  provide  at  any  section  at  least  the  same  amount  of 
metal  as  has  been  lost  in  making  the  opening.  In  the  boiler  illustrated  on  Plate  XII. 
the  butt-straps  serve  also  as  strengthening-plates  around  the  manholes  and  where  tie- 
rods  pass  through  the  front-head. 

It  is  recommended  to  place  the  larger  axis  of  manholes  in  a  transverse  direction  on 
circular  shells,  so  that  the  least  metal  is  cut  away  in  the  direction  in  which  the  stress  on 
the  shell  is  greatest. 

The  precautions  to  be  taken  when  steam-domes  are  placed  on  cylindrical  shells  will 
be  discussed  in  section  2,  chapter  xiii. 

For  the  shell  of  boilers  an  inferior  sort  of  iron  is  often  used,  known  as  "  shell-iron," 
which  does  not  flange  well ;  but  for  the  boilers  of  United  States  naval  vessels  it  is 
always  stipulated  that  all  parts  shall  be  constructed  of  the  best  charcoal  flange-iron. 

2.  Rectangular  Shells. — The  form  of  boilers  generally  used  in  vessels  of  the 
United  States  Navy,  in  cases  where  the  steam-pressure  does  not  exceed  45  Ibs.  above 
the  atmosphere,  is  illustrated  on  Plates  III.,  VI.,  VII.,  and  XVII.  The  top,  bottom, 
sides,  front,  and  back  of  the  shell  are  flat ;  but  the  sheets  joining  the  top  to  the  sides, 
front,  and  back,  and  the  sides  and  back  to  the  bottom,  are  bent  to  as  large  a  radius  as 
the  internal  arrangement  of  the  boiler  admits.  By  giving  to  the  lower  part  of  the  boiler 
the  form  shown  on  Plate  XVII.  there  is  not  only  a  useless  space  in  the  boiler  omitted, 
but  a  great  additional  advantage  is  often  gained  in  narrow  vessels,  since,  with  the  fire- 
room  running  in  a  fore-and-aft  direction  between  the  boilers,  these  can  be  placed  much 
farther  outboard.  Rectangular  boilers  are  often  made  without  water-bottoms  (see 
Plates  VI.,  VII.) ;  this  form  will  be  described  in  section  5  of  the  present  chapter. 

The  thickness  of  the  plates  of  rectangular  boiler-shells  varies  ordinarily  from  ^  to 
-fa  inch,  according  to  their  location,  the  steam-pressure,  and  the  arrangement  of  the 
stays  and  braces.  The  plates  forming  the  lower  portion  of  the  shell  exposed  to  the  cor- 
rosive action  of  the  bilge-water  are  made  tt  or  i  incn  thicker  than  the  rest.  Lap-joints 
are  generally  employed  throughout  the  shell  of  rectangular  boilers,  and  these  should  be 
double-riveted.  The  laps  are  sometimes  slightly  bent,  one  inward  and  the  other  out- 
ward, so  as  to  keep  the  sheets  forming  a  flat  surface  in  the  same  plane  ;  by  giving  in 
this  manner  to  the  lap-joints  the  form  which  they  tend  to  assume  under  pressure  the 
joints  are  less  severely  strained  (see  figure  46).  Care  must  be  taken  that  the  laps  of 
contiguous  sheets  break  joint,  and  that  they  are  accessible  for  calking.  In  the  horizon- 
tal joints  of  the  sides,  front,  and  back  the  lap  of  the  upper  end  of  each  sheet  is  placed 


216  STEAM  BOILERS.  CHAP.  IX. 

on  the  outside  of  the  boiler ;  this  prevents  the  loose  scale  from  lodging  on  the  laps  in- 
side the  boiler.  The  square  corners  connecting  the  sides,  front,  and  back  of  the  boiler 
are  formed  by  turning  flanges  on  the  sheets.  The  practice  of  forming  these  corners  by 
angle-irons  placed  inside  the  boiler,  to  which  the  plates  are  riveted,  permits  the  use  of 
an  inferior  iron  for  the  shell,  but  is  not  to  be  recommended. 

Plates  VI.,  VII.,  XVII.  illustrate  fully  the  construction  of  the  shell  of  rectangular 
boilers,  showing  the  size  and  shape  of  the  plates  and  the  manner  of  forming  the  flanges 
and  joints.  An  English  practice  of  welding  the  plates  forming  the  boiler-front  has  been 
described  and  illustrated  in  chapter  viii. 

3.  Cylindrical  Shells. — Cylindrical  shells  are  generally  built  up  by  joining  to- 
gether several  rings  or  belts.  The  plates  forming  these  belts  are  so  arranged  that  the 
fibre  of  the  iron  runs  in  a  circumferential  direction.  When  plates  of  moderate  thick- 
ness are  used  the  longitudinal  seams  are  often  formed  by  double-riveted  lap-joints  ;  it 
is,  however,  better  to  use  double-riveted  butt-joints  with  an  inner  and  outer  covering- 
plate.  Sometimes  these  rings  are  formed  by  welding  the  plates  together.  In  connect- 
ing these  several  belts  care  must  be  taken  that  the  longitudinal  seams  of  adjoining  belts 
are  placed  as  far  apart  as  possible. 

The  transverse  joints  connecting  these  belts  are  either  lap  or  butt  joints.  When  the 
belts  are  connected  by  lap-joints  it  may  be  advantageous  to  place  them  telescopically, 
as  shown  in  figure  18,  in  short  cylindrical  boilers  with  few  widths,  since  that  arrange- 
ment tends  to  drain  the  mud  and  dampness  toward  the  large  end,  where  cocks,  hand- 
holes,  or  other  provisions  may  be  made  for  cleaning.  When  the  boilers  are  long  the 
sheets  are  alternately  outside  and  inside,  or  raised  and  sunken.  When  a  single  butt- 
strap  is  used  for  the  transverse  joints  it  must  be  placed  on  the  outside  of  the  shell,  in 
order  to  make  it  accessible  for  calking ;  the  inner  longitudinal  butt-straps  must  lap 
over  on  the  adjoining  sheets,  so  that  the  ends  of  these  straps  may  be  calked  properly 
(see  Plate  XIII.)  Single  butt-straps  give  ample  strength  for  the  transverse  joints  of 
shells ;  sometimes,  however,  a  thin  inner  strap  is  added,  in  order  to  give  facilities  for  calk- 
ing the  joint  more  thoroughly  from  the  inside.  It  is  well  to  put  a  rivet  through  the  seam 
at  places  where  the  longitudinal  and  transverse  joints  meet,  in  order  to  close  them  effec- 
tually against  any  leakage.  The  ends  of  the  transverse  butt-straps  are  made  to  lap  over 
one  another,  the  inner  end  being  properly  scarfed.  The  riveting  of  these  transverse 
straps  to  the  belts  is  commenced  at  their  middle,  so  that  any  slack  may  be  worked  into 
the  seam.  Where  the  longitudinal  straps  are  crossed  by  the  transverse  straps  their 
ends  are  scarfed,  so  that  they  all  lie  close  together  and  against  the  shell,  and  the  trans- 
verse strap  requires  less  setting. 


SBC.  3.  SHELL,  FURNACES,  AND  BACK-CONNECTIONS.  217 

The  front  and  back  heads  of  large  boilers  are  flat,  and  are  flanged  in  order  to  connect 
them  to  the  shell.  In  small  boilers  these  flanges  are  often  placed  outside  the  shell 
when  the  space  inside  the  boiler  is  too  contracted  to  be  accessible  for  riveting  ;  but  in 
large  boilers  these  flanges  are  turned  inside  the  boiler,  so  that  the  joint  can  be  calked 
inside  and  outside.  Angle-irons  are  sometimes  used  to  make  this  connection.  The 
heads  of  large  boilers  are  necessarily  composed  of  several  plates,  connected  either  by 
lap-joints  or  by  butt-joints.  When  lap-joints  are  used  the  laps  of  the  same  plate  are 
either  placed  one  inside  and  the  other  outside,  or  the  plates  are  placed  in  alternate  in- 
side and  outside  courses.  When  the  plates  composing  the  heads  are  thick  it  is  best  to 
unite  them  by  means  of  a  double-riveted  single  butt-strap  placed  on  the  outside.  The 
ends  of  the  butt-strap  are  bent  with  the  flange  of  the  head  and  thinned,  the  cylindrical 
shell  being  set  out,  where  it  covers  the  strap,  in  order  to  make  a  close-fitting,  tight 
joint. 

'Lloyd's  Register  of  British  and  Foreign  Shipping'  prescribes  the  following 
"Rules  for  Determining  the  Working  Pressure  in  New  Boilers": 

Cylindrical  Shells. — The  strength  of  circular  shells  to  be  calculated  from  the  actual 
strength  of  the  longitudinal  joint  by  the  following  formula : 

Cx  Tx  B 

—p: —  -  =  working  pressure, 

where  C  =  constant  as  per  following  table  ; 
T=  thickness  of  plates  in  inches  ; 
D  —  mean  diameter  of  shell  in  inches  ; 

B  =  percentage  of  strength  of  joint  found  as  follows— the  least  percentage 
to  be  taken : 

For  plate  at  joint  B  =  ^^-  X  100 ; 

For  rivets  at  joint  B  =  -    ^  X  100  with  punched  holes  ; 

B  =  — X~  X  90  with  drilled  holes 
p  X  T 

(in  case  of  rivets  being  in  double-shear  1.75  a  is  to  be  used  instead  of  a) ; 
where  p  =  pitch  of  rivets  ; 

d  —  diameter  of  rivets  ; 
a  =  sectional  area  of  rivets  ; 
n  =  number  of  rows  of  rivets. 
NOTE. — In  steel  boilers  it  is  required  that  the  strength  of  the  rivets  used  to  resist 


21S 


STEAM  BOILERS. 


CHAP.  IX. 


shearing  should  be  shown  to  be  at  least  26  tons  per  square  inch.     If  it  is  less  than  26 
tons  per  square  inch  the  rivet-area  should  be  proportionately  increased. 


TABLE  OF  CONSTANTS. 
IRON  BOILERS. 


Description  of  longitudinal  joint. 

For  plates  '/,  inch 
thick  and 
under. 

For  plates  %  inch 
thick  and  above 
1/2  inch. 

For  plates  above  % 
inch  thick. 

155 
170 
IJO 
I  80 

165 
1  80 
1  80 
190 

170 
190 
190 
2OO 

"           drilled  holes  

Double  butt-strap  joint,  punched  holes..  .  . 
'                  "            drilled  holes  

STEEL  BOILERS. 


Description  of  longitudinal  joint. 

For  plates  % 
inch  thick 
and  under. 

For  plates  9-16 
inch  thick 
and  above  % 
inch. 

For  plates  % 
inch  thick 
and  above  9-16 
inch. 

For  plates 
above  %  inch 
thick. 

2OO 
215 

215 
230 

230 

250 

240 
260 

Double  butt-strap  joints  

NOTE. — The  inside  butt-strap  to  be  at  least  three-quarters  the  thickness  of  the  plate. 

For  the  shell-plates  of  superheaters  or  steam-chests  exposed  to  the  direct  action  of 
the  flame  the  constants  should  be  two-thirds  of  those  given  in  the  above  tables. 

Proper  deductions  are  to  be  made  for  openings  in  shell. 

All  manholes  in  circular  shells  to  be  stiffened  with  compensating-rings. 

The  shell-plates  under  domes  in  boilers  so  fitted  to  be  stayed  from  the  top  of  the 
dome  or  otherwise  stiffened. 

The  '  Surveyors  of  the  Board  of  Trade '  (England)  are  guided  in  the  inspection  of 
boilers  by  the  following  rules : 

"  When  cylindrical  boilers  are  made  of  the  best  material,  with  all  the  rivet-holes 
drilled  in  place  and  all  the  seams  fitted  with  double  butt-straps,  each  of  at  least  five- 
eighths  the  thickness  of  the  plates  they  cover,  and  all  the  seams  at  least  double-riveted 
with  rivets  having  an  allowance  of  not  more  than  50  per  cent,  over  the  single-shear,  and 
provided  that  the  boilers  have  been  open  to  inspection  during  the  whole  period  of  con- 
struction, then  six  may  be  used  as  the  factor  of  safety  ;  but  the  boilers  must  be  tested  by 
hydraulic  pressure  to  twice  the  working  pressure  in  the  presence  and  to  the  satisfaction 
of  the  Board's  surveyors.  But  when  the  above  conditions  are  not  complied  with  the 


SEC.  3. 


SHELL,  FURNACES,  AND  BACK-CONNECTIONS. 


219 


additions  in  the  following  scale  must  be  added  to  the  factor  six,  according  to  the  cir- 
cumstances of  each  case : 


A 
B 
C 
D 

E* 
F 

G 

H 
I 

J* 
K 

L 
M 
N 
O 
P 

Q 

R 

S 
T 
U 


W* 
X* 


•3 
•3 

•5 

•75 
.1 

•i5 
•'5 

.2 

.2 

.2 

.1 

•3 

-15 
.1 

.1 

.2 
.1 

.1 
.2 

•25 


•4 
•4 

1.65 


To  be  added  when  all  the  holes  are  fair  and  gpod  in  the  longitudinal  seams,  but 

drilled  out  of  place  after  bending. 
To  be  added  when  all  the  holes  are  fair  and  good  in  the  longitudinal  seams,  but 

drilled  out  of  place  before  bending. 
To  be  added  when  all  the  holes  are  fair  and  good  in  the  longitudinal  seams,  but 

punched  after  bending,  instead  of  drilled. 
To  be  added  when  all  the  holes  are  fair  and  good  in  the  longitudinal  seams,  but 

punched  before  bending. 

To  be  added  when  all  the  holes  are  not  fair  and  good  in  the  longitudinal  seams. 
To  be  added  if  the  holes  are  all  fair  and  good  in  the  circumferential  seams,  but 

drilled  out  of  place  after  bending. 
To  be  added  if  the  holes  are  fair  and  good  in  the  circumferential  seams,  but  drilled 

before  bending. 
To  be  added  if  the  holes  are  fair  and  good  in  the  circumferential  seams,  but  punched 

after  bending. 
To  be  added  if  the  holes  are  fair  and  good  in  the  circumferential  seams,  but  punched 

before  bending. 

To  be  added  if  the  holes  are  not  fair  and  good  in  the  circumferential  seams. 
To  be  added  if  double  butt-straps  are  not  fitted  to  the  longitudinal  seams,  and  the 

said  seams  are  lap  and  double  riveted. 
To  be  added  if  double  butt- straps  are  not  fitted  to  the  longitudinal  seams,  and  the 

said  seams  are  lap  and  treble  riveted. 
To  be  added  if  only  single  butt-straps  are  fitted  to  the  longitudinal  seams,  and  the 

said  seams  are  double-riveted. 
To  be  added  if  only  single  butt-straps  are  fitted  to  the  longitudinal  seams,  and  the 

said  seams  are  treble-riveted. 

To  be  added  when  any  description  of  joint  in  the  longitudinal  seams  is  single- 
riveted. 
To  be  added  if  the  circumferential  seams  are  fitted  with  single  butt-straps  and  are 

double-riveted. 
To  be  added  if  the  circumferential  seams  are  fitted  with  single  butt-straps  and  are 

single-riveted. 
To  be  added  if  the  circumferential  seams  are  fitted  with  double  butt-straps  and  are 

single-riveted. 

To  be  added  if  the  circumferential  seams  are  lap-joints  and  are  double-riveted. 
To  be  added  if  the  circumferential  seams  are  lap-joints  and  are  single-riveted. 
To  be  added  when  the  circumferential  seams  are  lap  and  the  streaks  or  plates  are 

not  entirely  under  or  over. 

To  be  added  when  the  boiler  is  of  such  a  length  as  to  fire  from  both  ends,  or  is  of  un- 
usual length,  such  as  flue-boilers  ;  and  the  circumferential  seams  are  fitted  as  de- 
scribed opposite  P,  R,  and  S ;  but,  of  course,  when  the  circumferential  seams  are 

as  described  opposite  Q  and  T,  V-3  will  become  ¥.4. 
To  be  added  if  the  seams  are  not  properly  crossed. 
To  be  added  when  the  iron  is  in  any  way  doubtful  and  the  surveyor  is  not  satisfied 

that  it  is  of  the  best  quality. 
To  be  added  if  the  boiler  is  not  open  to  inspection  during  the  whole  period  of  its 

construction. 


220  STEAM  BOILERS.  CHAP.  IX. 

"Where  marked  *  the  allowance  may  be  increased  still  further  if  the  workmanship 
or  material  is  very  doubtful  or  very  unsatisfactory 

"  The  strength  of  the  joints  is  found  by  the  following  method  : 

(Pitch  —  diameter  of  rivets)  x  100  _    j  Percentage  of  strength  of  plate  at  joint 
Pitch  '   {       as  compared  with  the  solid  plate. 

(Area  of  rivets  X  No.  of  rows  of  rivets)  x  100  _    (  Percentage  of  strength  of  rivets  as 
Pitch  x  thickness  of  plate  :   (     compared  with  the  solid  plate.* 

"Then  take  iron  as  equal  to  23  tons,  and  use  the  smallest  of  the  two  percentages  as 
the  strength  of  the  joint,  and  adopt  the  factor  of  safety  as  found  from  the  preceding 
scale : 

(51520  X  percentage  of\          /twice  the  thickness  of\ 
strength  of  joint.      I         I   the  plate  in  inches.    J  Pressure  to  be  allowed  per 

=F — n — =r,  -Vrr — r~ri — •    •  ~e — rz~  =  \      square  inch  on  the  safe- 

Inside  diameter  of  the  boiler  in  inches  x  factor  of  safety      |     ty-valves. 

"Plates  that  are  drilled  in  place  must  be  taken  apart  and  the  burr  taken  off,  and 
the  holes  slightly  countersunk  from  the  outside. 

"Butt-straps  must  be  cut  from  plates  and  not  from  bars,  and  must  be  of  as  good  a 
quality  as  the  shell-plates,  and  for  the  longitudinal  seams  must  be  cut  across  the  fibre. 
The  rivet-holes  may  be  punched  or  drilled  when  the  plates  are  punched  or  drilled  out 
of  place,  but  when  drilled  in  place  must  be  taken  apart  and  the  burr  taken  off,  and 
slightly  countersunk  from  the  outside. 

"  When  single  butt-straps  are  used,  and  the  rivet-holes  in  them  punched,  they  must 
be  one-eighth  thicker  than  the  plates  they  cover. 

"The  diameter  of  the  rivets  must  not  be  less  than  the  thickness  of  the  plates  of  which 
the  shell  is  made  ;  but  it  will  be  found  when  the  plates  are  thin,  or  when  lap-joints  or 
single  butt-straps  are  adopted,  that  the  diameter  of  the  rivets  should  be  in  excess  of  the 
thickness  of  the  plates.  Dished  ends  that  are  not  truly  hemispherical  must  be  stayed ; 
if  they  are  not  theoretically  equal  in  strength  to  the  pressure  needed  they  must  be 
stayed  as  flat  surfaces,  but  if  they  are  theoretically  equal  in  strength 'to  the  pressure 
needed  the  stays  may  have  a  strain  of  10,000  Ibs.  per  effective  square  inch  of  sectional 
area. 

"  Surveyors  will  remember  that  the  strength  of  a  sphere  to  resist  internal  pressure  is 
double  that  of  a  cylinder  of  the  same  diameter  and  thickness. 

"All  manholes  and  openings  must  be  stiffened  with  compensating-rings  of  at  least  the 
same  effective  sectional  area  as  the  plates  cut  out,  and  in  no  case  should  the  plate-rings 

*  If  the  rivets  are  exposed  to  double-shear  multiply  the  percentage  as  found  by  1.5. 


SEC.  4  SHELL,  FURNCAES,  AND  BACK-CONNECTIONS.  221 

be  less  in  thickness  than  the  plates  to  which  they  are  attached.  The  openings  in  the 
shells  of  cylindrical  boilers  should  have  their  shorter  axes  placed  longitudinally.  It  is 
very  desirable  that  the  compensating-rings  round  openings  in  flat  surfaces  be  made  of 
L  or  T  iron." 

4.  Furnaces. — The  plates  used  in  the  construction  of  the  furnaces  should  be  made 
as  thin  as  is  consistent  with  proper  strength  and  stiffness,  because  thick  plates  are 
liable  to  blister  when  exposed  to  the  intense  heat  of-  the  fire.  For  the  same  reason  as 
few  seams  as  possible  are  used  in  the  furnace  and  back-connection,  and  the  lap-joints 
are  single-riveted.  The  laps  should  be  placed  in  such  a  direction  that  the  current  of 
the  products  of  combustion  does  not  strike  the  edge  of  the  plate,  and  that  there  is  no 
tendency  for  the  scale  to  lodge  and  accumulate  at  any  place  exposed  to  an  intense  heat. 
The  furnace-crown  should  have  as  little  bracing  as  practicable,  and  the  attachments  of 
the  stays  and  braces  should  be  of  such  a  form  that  they  interfere  as  little  as  possible 
with  the  circulation  of  the  water,  and  do  not  serve  as  a  nucleus  for  an  excessive  accu- 
mulation of  scale. 

For  furnaces  special  brands  of  iron,  known  as  "fire-box"  and  "extra  fire-box"  iron, 
are  used,  which  are  specially  fitted  to  withstand  the  oxidizing  and  wasting  influence  of 
intense  heat  and  the  impact  of  flame.  The  furnaces  of  all  boilers  built  for  the  English 
Admiralty  are  made  of  "Low  Moor"  or  "Bowling"  iron.  It  is  essential  that  the  iron 
used  for  furnaces  should  be  free  from  all  lamination.  The  use  of  mild  steel  for  fur- 
naces is  advantageous  especially  on  account  of  its  homogeneous  structure ;  it  is,  how- 
ever, necessary  to  exercise  great  care  in  the  selection  and  use  of  steel  for  furnaces,  since 
in  many  instances  the  steel  plates  of  furnaces  and  fire-boxes  have  cracked  after  having 
been  in  use  a  short  time,  although  the  material  was  of  a  mild  quality  and  stood  the 
tempering-test  well. 

Copper  has  been  used  extensively  for  locomotive  fire-boxes,  especially  in  Europe,  on 
account  of  its  homogeneous  structure  and  high  thermal  conductivity,  but  it  is  not  used 
for  marine  boilers. 

Yaiious  devices  have  been  proposed  for  increasing  the  heating-surface  of  the  fur- 
nace, but  nearly  all  of  them  interfere  to  so  great  an  extent,  with  the  removal  of  the 
scale  or  with  the  cleaning  of  the  fire,  besides  presenting  difficulties  of  construction, 
that  they  are  almost  unknown  in  practice. 

The  corrugated  boiler-flues  made  by  the  Leeds  forge  Company  (England),  under 
the  patents  of  S.  Fox,  have  come  into  extensive  use  of  late,  and  have  generally  given 
satisfaction.  In  some  cases  iron  corrugated  furnace-flues  have  shown  signs  of  blister- 
ing after  having  been  in  use  a  short  time  ;  but  this  is  ascribed  to  original  defects  in  the 


222  STEAM  BOILERS.  CHAP.  IX. 

plates,  and  not.  to  any  injurious  effect  of  the  process  of  manufacture.  Corrugated  flues 
have  borne  test-pressures  more  than  twice  as  great  as  the  pressures  at  which  plain  cylin- 
drical flues,  made  of  the  same  material  and  of  equal  dimensions,  collapsed.  The  great 
resistance  to  collapse  of  corrugated  flues  of  an  oval  cross-section,  compared  with  that  of 
plain  oval  flues,  is  of  special  importance."  These  corrugated  flues  possess  great  longi- 
tudinal elasticity,  and  thus  accommodate  themselves  readily  to  differences  of  pressure 
and  temperature,  rendering  the  flat  plates  of  the  boiler-front  and  back-connection  to 
which  they  are  fastened  less  liable  to  grooving.  This  longitudinal  elasticity  prevents 
thick  scale  from  adhering  firmly  to  the  metal,  and  thus  the  surfaces  of  the  tubes  are 
always  kept  clean ;  by  this  fact  the  greater  evaporative  efficiency  claimed  for  corru- 
gated boiler-flues  may  perhaps  be  explained. 

These  flues  are  made  either  of  the  best  Yorkshire  iron  or  of  Siemens-Martin  steel  of 
a  very  mild  quality.  The  plate  is  first  bent  to  a  cylinder  and  welded  by  machinery  ; 
then  the  circumferential  corrugations  are  rolled  in.  It  is  proposed  to  roll  solid  steel 
tubes  without  welds  from  seamless  circular  blooms  under  S.  Fox's  patents. 

The  following  data  in  reference  to  tests  of  S.  Fox's  corrugated  boiler-flues  are  given 
in  Engineering,  March,  1878,  and  June,  1880  :  .- 

A  flue  made  of  welded  steel,  f  inch  thick,  had  thirteen  corrugations  in  a  length  of  6 
feet  J  inch  between  extreme  centres,  giving  a  mean  pitch  of  6.03  inches.  The  depth  of 
the  corrugations  was  1  £  inches,  and  the  mean  least  diameter  of  the  flue  was  about  33| 
inches.  There  was  at  each  end  a  plain  part  extending  12f  inches  beyond  the  end  corru- 
gations ;  these  plain  parts  were  packed  in  the  end  plates  of  the  test-cylinder  by  cupped 
leather  rings.  In  this  manner  the  flue  was  quite  free  to  move  longitudinally. 

The  flue  bore  a  hydraulic  pressure  of  550  Ibs.  per  square  inch  without  showing  any 
permanent  set.  At  a  pressure  of  600  Ibs.  the  flue  began  to  fail,  but  retained  a  symme- 
trical oval  form,  the  difference  of  the  longer  and  shorter  diameters  being  about  5  inches. 
This  oval  flue,  being  again  tested,  gave  way  at  a  pressure  of  350  Ibs. 

A  welded  iron  flue,  f  inch  thick,  having  a  mean  least  diameter  of  about  35£  inches, 
and  having  circumferential  corrugations  1^  inches  deep  and  6  inches  pitch,  was  tested 
in  the  same  apparatus,  and  gave  way  by  general  distortion  as  a  pressure  of  450  Ibs.  was 
approached. 

A  plain  cylindrical  flue,  made  of  the  same  material,  f  inch  thick,  and  having  a  mean 
horizontal  diameter  of  36.63  inches  and  a  mean  vertical  diameter  of  36.98  inches,  came 
down  like  a  blister  on  the  top  at  a  pressure  of  200  Ibs.  while  being  tested  in  the  same 
apparatus. 

Corrugated  plates  are  also  coming  into  use  for  the  fire-boxes  of  portable  and  locomo- 


SEC.  5. 


SHELL,  FURNACES,  AND  BACK-CONNECTIONS. 


223 


Fig.  93. 


Fig.  94. 


; 

• 


WWWWWVi 


tive  boilers  in  England.  In  Garrefs  portable  engine  boilers  the  top  of  the  rectangular 
fire-box  is  made  with  several  deep  corrugations  extending  lengthwise  the  furnace.  The 
Leeds  Forge  Company  are  building  portable  and  locomotive  boilers  the  semi-cylindri- 
cal top  and  flat  sides  of  which  are  stayed  by  a  new  system  of  diagonal  corrugations 
patented  by  Fox  and  Greig.  The  external  shell  around  the  fire-box  is  corrugated  in 
the  same  manner,  and  the  use  of  stay-bolts  and  sling-stays  is  dispensed  with. 

5.  Furnaces  of  Rectangular  Boilers. — Furnaces  of  rectangular  or  semi-cylin- 
drical boilers  have  generally  flat,  vertical  sides  joined 
to  a  flat  bottom  by  corners  curved  to  a  short  radius, 
and  to  a  more  or  less  arched  crown. 

A  flat  furnace-crown  is  not  only  the  weakest 
form,  requiring  very  heavy  bracing,  but  interferes 
greatly  with  the  proper  circulation  of  the  water. 
Figures  93,  94  are  intended  to  illustrate  the  circu- 
lation of  the  water  with  flat  and  arched  furnace- 
crowns  respectively,  the  dotted  lines  representing 
the  ascending  bubbles  of  steam,  and  the  arrows  in- 
dicating the  direction  of  the  currents  of  water  flowing  in  to  fill  the  vacant  space.  Flat 
furnace-crowns  have  the  advantage  of  making  the  furnaces  roomy  over  the  grate,  and 
are  used  generally  in  locomotives,  in  which  heavier  bracing  can  be  used  with  safety  on 
the  furnace-crown  than 
in  marine  boilers,  since 
they  are  less  liable  to 
be  injured  by  incrusta- 
tions. In  marine  boil- 
ers, carrying  a  mode- 
rate steam  -  pressure, 
the  furnace-crown  has 
often  the  form  of  a  flat 
arch ;  in  this  case  the 
crown-sheet  is  lap- 
jointed  to  the  flat  sides; 
sometimes  the  arched 
crown-sheet  is  bent  to 


o 


o 


o 


o 


o 


o 


o 


o 


r 


Fig.  95, 


a  shorter  radius  where  it  is  joined  to  the  sides,  as  in  figure  95. 

The  form  of  furnaces  commonly  used  in  United  States  naval  vessels  is  illustrated  on 


224 


STEAM  BOILERS. 


CHAP.  IX. 


Plates  VI. ,  VII.,  XVII.  The  semi-cylindrical  form  of  the  furnace-crown  gives  a  much 
less  roomy  furnace,  but  it  makes  the  inside  of  the  boiler  much  more  accessible  for  the 
same  height  of  boiler,  and  requires  scarcely  any  bracing.  In  this  case  the  whole  crown 
and  the  straight  sides  of  the  furnace  may  be  made  in  one  piece,  so  that  no  seams  occur 
in  the  furnace  except  at  the  ends  and  below  the  grate  ;  but  often  the  crown-sheet  con- 
sists of  two  plates  connected  by  a  transverse  seam  in  the  middle  of  the  furnace.  When 
it  is  necessary  to  use  longitudinal  seams  within  the  furnace  above  the  grate  they  should 
never  be  placed  near  the  line  of  fire,  but  (as  in  Plate  XVII.)  near  the  top  of  the  crown, 
far  enough  to  one  side  to  clear  the  foot  of  the  braces.  The  fibre  of  the  plates  forming 
the  furnace  runs  generally  circumferentially. 

The  flanges  required  to  secure  the  furnace  in  the  boiler  at  the  front  and  back  are 
generally  not  turned  on  the  plates  forming  the  furnace  ;  in  some  English  and  French 
boilers  a  flange  is  turned  outward  on  the  back  end  of  the  furnace-crown,  to  a  radius  of 
four  or  five  inches,  to  connect  it  with  the  back  tube-sheet.  With  this  method  of  fasten- 
ing the  movements  due  to  the  expansion  and  contraction  of  the  furnace  and  of  the  tubes 
tend  to  spring  the  joint  open  and  cause  leaks,  unless  the  flange  is  made  sufficiently  flex- 
ible by  the  large  radius  with  which  it  is  turned.  Angle-irons  are  frequently  used  in 
English  and  French  practice  for  securing  the  furnace  at  the  front  and  back  in  the  boiler. 
The  cheapest  way  of  securing  the  furnace  to  the  front  of  the  boiler  is  to  cut  out  the 
front  plate  equal  to  the  cross-section  of  the  furnace,  rivet  an  angle-iron  around  this 
opening,  inside  or  outside  the  shell,  and  secure  the  furnace  to  this  angle-iron.  Cast- 
iron  frames,  to  which  the  furnace  and  ashpit  doors  are  attached,  are  bolted  to  the  front 
of  the  boiler  around  the  furnace-opening.  These  large  frames  are  apt  to  warp  and 

crack,  and  give  much  trouble.  On 
this  account  the  furnace-mouth  is 
contracted  in  many  French  and  Eng- 
lish boilers  by  flanging  the  furnace 
crown-sheet  downward  in  the  manner 
shown  in  figure  95. 

Sometimes  the  crown-sheet  is  made 
to  slope  downward  to  the  front  of  the 
boiler,  as  illustrated  in  figures  96,  97, 

in  order  to  gain  room  under  the  front- 

lgl     '  connection,  when  the  boiler  is  neces- 

sarily low.  This  can  be  done  without  impairing  the  efficiency  of  the  furnace,  since  more 
height  is  required  over  the  grate  at  the  back  than  at  the  front. 


SEC.  5. 


SHELL,  FDBNACES,  AND  BACK-CONNECTIONS. 


225 


Fig.  97. 


Figure  96  represents  the  furnace  of  a  tubular  marine  boiler  built  by  Laird  &  Son, 
Birkenhead,  England  ;  and  figure  97  represents  the  furnace  of  a  boiler  for  the  United 
States  tugboat  Glance,  built  in  1879. 

When  the  water-spaces  are  too  narrow  to  connect  the  furnace  to  the  shell  by  flanges 
turned  on  the  respective  plates,  or  by  special  flanged  pieces  as  around  the  furnace- 
door  opening  in  figure  97,  the 
connection  is  formed  either 
by  placing  a  frame,  formed 
by  bending  and  welding  a 
wrought  -  iron  bar  of  square 
cross-section  to  the  required 
shape,  between  the  furnace  and 
the  shell,  and  riveting  the  plates 
to  the  frame  by  through-rivets 
(as  at  the  bottom  of  the  boiler 
in  figure  96,  and  around  the 
furnace  door-opening  in  figure 
1,  Plate  XXVIII.),  or  by  bend- 
ing the  plate  of  the  furnace 
with  an  easy,  reverse  curve 
outward,  and  riveting  it  directly  to  the  shell  (as  at  the  bottom  of  the  boilers  represented 
on  Plate  XXVIII.) . 

The  usual  method  of  securing  the  furnace  used  in  boilers  of  United  States  naval 
vessels  is  illustrated  on  Plates  VI.,  VII.,  and  XVII.  An  opening  of  the  size  and  shape 
required  for  the  furnace-door  and  ashpit  is  formed  in  the  boiler-front,  a  flange  being 
turned  inward  around  this  opening.  The  crown-sheet  and  sides  of  the  furnace  are 
riveted  to  a  separate  flanged  piece,  which  has  an  opening  corresponding  to  the  furnace- 
door  opening  of  the  boiler-front,  but  is  flanged  outward  around  this  opening.  A  narrow 
strip  is  riveted  inside  the  furnace-door  opening  to  the  flanges  of  the  boiler-front  and 
of  the  furnace  front -piece. 

The  bottom  of  the  furnace  of  rectangular  boilers  is  sometimes  arched  downward ; 
but  the  flat  bottom,  illustrated  on  Plate  XVII.,  is  best  adapted  for  supporting  the  flat 
bottom  of  the  boiler  by  stay-bolts,  while  the  curved  corners  give  additional  room  in  the 
water-space  for  collecting  solid  matter  and  for  cleaning  out  the  water-legs  and  the 
water-bottom  through  the  handholes. 

The  principal  use  of  the  water-bottom  is  to  form  a  convenient  ashpan,  which  does 


226 


STEAM  BOILERS. 


CHAP.  DC 


not  become  overheated  and  warped  by  the  heat  radiated  through  the  grate  and  by  the 
fire  falling  through  the  bars  ;  it  serves  also  as  a  receptacle  for  mud,  broken  scale,  and 
other  solid  matter  entering  the  boiler  with  the  feed- water.  The  water-bottom  is  gene- 
rally one  of  the  first  parts  to  give  out  in  marine  boilers  through  internal  and  external 
corrosion,  and  it  is  in  many  cases  inaccessible  for  thorough  repair  while  the  boilers  re- 
main in  the  vessel.  On  this  account  they  are  often  omitted,  and  separate  cast-iron  or 
wrought-iron  ashpans  are  placed  under  each  furnace.  The  weight  of  these  so-called 
dry-bottom  boilers,  including  the  supports  and  ashpans,  is  about  the  same  as  that  of  the 
water-bottom  boilers,  including  the  additional  amount  of  water  carried  by  them  ;  but 
the  former  are  somewhat  cheaper  to  construct.  To  prevent  the  over-heating  and  warp- 
ing of  the  ashpans  of  dry -bottom  boilers  water  has  to  be  kept  in  them.  Although  they 
deteriorate  rapidly,  the  durability  of  the  boiler  is  not  impaired  thereby  as  by  the  corro- 
sion of  the  water-bottoms.  The  durability  of  the  latter  is  increased  by  giving  to  the 
plates  an  additional  thickness  in  order  to  allow  for  corrosion. 

To  form  the  water-legs  of  the  dry-bottom  boiler  the  sides  of  the  furnaces,  carried 
some  distance  below  the  grates,  are  connected  at  the  bottom  by  a  separate  curved  plate. 
The  lap  of  this  plate  is  often  placed  inside  the  boiler ;  by  placing  it  on  the  outside  the 
joint  is  made  more  accessible  for  calking  while  the  boiler  remains  in  position  in  the 
ship,  and  some  additional  room  is  gained  in  the  water-leg.  Sometimes  the  water-legs 
are  enlarged  at  the  bottom  to  make  them  more  accessible  for  cleaning ;  they  must  ex- 
tend far  enough  below  the  grate  so  that  there  is  no  danger  of  their  becoming  filled  with 

solid  matter  up  to  the  line  of  fire.  It  is  well  to 
let  the  bottom  of  the  water-space  running  length- 
wise at  the  back  of  the  boiler  terminate  in  a  cylin- 
drical drum,  unobstructed  by  stays  and  accessi- 
ble through  manholes  placed  at  the  ends  for 
cleaning  and  repairs  (see  figure  98). 

6.  Cylindrical  Furnaces. — The  furnaces  of 
cylindrical  boilers  calculated  to  carry  steam  of  a 
high  pressure  are  made  of  a  circular  cross-sec- 
tion. In  chapter  vi.  the  laws  governing  the  col- 
lapsing strength  of  cylindrical  flues  have  been 
investigated,  and  the  importance  of  making  their  cross-section  perfectly  circular  has 
been  pointed  out.  For  this  reason  the  furnace-flues  are  generally  made  with  longitudi- 
nal butt-joints,  and  not  with  lap-joints.  The  strap  is  placed  inside  the  flue  at  the  side 
and  below  the  grate,  so  as  to  be  accessible  for  calking,  not  to  come  in  contact  with  the 


r 


Fig.  98. 


SBC.  6. 


SHELL,  FURNACES,  AND  BACK-CONNECTIONS. 


227 


Fig.  99. 


fire,  and  not  to  be  in  the  way  of  hauling  the  ashes.     It  is  still  better  to  weld  the  longi- 
tudinal seams  in  the  manner  described  in  section  20,  chapter  viii. 

The  necessity  of  stiffening  long  flues  by  flanges  or  by  riveting  bands  around  them  at 
intervals  has  been  demonstrated  in  chapter  vi.  In  boilers  of  United  States  naval  vessels 
the  furnace-flues  are  generally  strengthened  by  means  of  the 
"Adamson"  joint  (see  figure  99  and  Plates  VIII.,  XL,  XII.) 
The  furnace-flue  consists  of  two  or  three  sections  flanged  outward  ; 
a  wrought-iron  ring,  about  f  thick,  is  placed  between  the  flanges, 
and  the  sections  are  connected  by  single-riveting.  There  are  no 
laps  or  rivets  in  contact  with  the  fire,  and  the  ring  or  welt  allows  the  joint  to  be  calked 
from  the  inside  and  outside.  This  flanging  can  be  done  only  with  very  good  iron  ;  in 
some  boiler- works  it  is  done  by  machinery  in  one  or  two  heats,  which  distresses  the 
plate  less  than  the  repeated  heating  with  the  common  method — an  important  advantage, 
especially  in  the  case  of  steel.  The  radius  at  the  root  of  the  flange  should  not  be  less 
than  f  inch  on  the  inside,  or  the  plate  will  be  liable  to  become  grooved  by  the  alternate 
expansion  and  contraction. 

Sometimes  the  several  lengths  of  the  furnace-flue  are  connected  by  T-iron  rings,  as 
shown  in  figure  100.     In  order  to  admit  of  calking  these 
joints  at  any  time  from  inside  the  furnace  a  clear  space 
of  at  least  one  inch  should  always  be  allowed  between  ^_^ 

the  ends  of  the  plates  ;  this  lessens  also  the  liability  to    ^^  J-  .          , — ,        . — 1  ,,,,,^ 
overheating  at  the  seam.     Accurate  workmanship  is  re- 
quired for  this  joint ;  the  two  lengths  of  tube  embraced  by  the  same  ring  must  be  of  ex- 
actly the  same  diameter  or  the  joint  will  give  trouble. 

In  order  to  allow  for  the  contraction  and  expansion  of  the  furnace-flue,  which  often 
cause  serious  trouble  by  grooving  in  long  boilers,  the  Bowling  hoop  has  been  intro- 


I  Fig.  100. 


Fig.  101. 


duced  (see  figure  101).  Like  the  T-iron  hoop,  it  has 
the  disadvantage  of  placing  a  double  thickness  of 
plate  and  the  rivet-heads  in  the  fire  at  the  joints. 

The  report  of  the  Chief-Engineer  of  the  Man- 
chester Steam-Users'  Association  for  the  year  1871 
contains  the  following  directions  regarding  the 

application  of  strengthening-hoops  to  the  flues  of  boilers  originally  made  without 

them : 

"The  hoops  should  be  of  angle-iron  section,  about  3"  X  3"  X  i".     They  should  be 

made  in  halves,  so  that  they  may  be  passed  in  at  the  manhole  and  then  riveted  to  the 


228  STEAM  BOILERS.  CHAP.  IX. 

furnace  or  flue  tubes  in  position,  thus  rendering  it  unnecessary  either  to  remove  the 
tubes  or  cut  any  opening  in  the  boiler.  The  angle-iron  should  not  be  brought  into 
direct  contact  with  the  plates  of  the  tube,  but  a  clear  space  of  not  less  than  one  inch 
should  be  left  between  the  two,  the  hoop  for  this  purpose  having  a  diameter  some  two 
inches  larger  than  the  furnace-tube  (see  figure  102).  The  hoop 
should  be  secured  to  the  furnace-tube  by  rivets  spaced  about  six 
inches  apart;  blocking-pieces,  through  which  the  rivets  should 


pass,  being  inserted  between  the  tube  and  the  angle-iron,  so  as  to 
give  a  solid  abutment  for  the  riveting,  while  the  halves  of  the  hoop 
should  be  connected  by  butt-straps  riveted  to  their  ends  at  the  back. 
.  .  .  The  blocking-pieces  should  be  made  of  a  strip  of  iron  not 
more  than  ^  inch  thick,  bent  round  into  a  circular  shape,  the  ends  being  welded  to- 
gether so  as  to  form  a  short  tube  or  ferrule.  These  ferrules  should  be  well  fitted  into 
the  space  between  the  hoop  and  the  plating  of  the  furnace  and  flue  tube,  while  the  ends 
of  one  half -hoop  should  be  firmly  butted  against  the  ends  of  the  other  half -hoop,  so 
that  the  whole  may  be  tightly  drawn  together,  as  much  of  the  support  afforded  by  these 
hoops  depends  on  their  being  made  one  with  the  furnace  and  flue  tubes,  and  not  put  in 
so  as  to  act  merely  as  separate  hoops  from  which  the  plates  are  hung.  .  .  . 

"A  hoop  of  angle-iron  is  preferable  to  one  of  T-iron,  as  the  single  flange  of  the 
angle-iron,  being  narrower  than  the  double  flange  of  the  T-iron,  offers  less  impediment 
to  the  escape  of  the  steam  generated  within  the  annular  space,  and  also  less  harborage 
for  deposit.  .  .  .  The  hoops  should  not  be  allowed  to  touch  the  shell  of  the  boiler,  or  the 
furnace-tubes  may  become  strained  and  leakage  be  induced,  since  furnace  and  flue 
tubes  rise  and  fall  with  variations  of  temperature,  and  thus  grind  against  the  sides  of 
the  shell  or  against  one  another  where  in  contact." 

Hoops  secured  in  the  foregoing  manner  should  be  used  only  when  their  addition  is 
an  after-consideration  ;  for  new  structures  one  of  the  joints  illustrated  in  figures  99, 100, 
and  101  should  be  used,  because,  as  has  been  pointed  out  in  section  3,  chapter  vi.,  it  is 
important  that  the  flanges  or  rings  supporting  a  flue  should  be  attached  to  it  rigidly 
around  its  whole  circumference,  and  not  merely  connected  with  it  at  detached  points. 
When  a  boiler  contains  several  furnaces  it  is  well  to  arrange  the  lengths  of  the  sections 
forming  the  flues  in  such  a  manner  that  the  flanges  or  strengthening-hoops  of  adjoining 
furnaces  are  about  six  inches  apart,  so  that  any  loose  scale  dropping  down  from  above 
does  not  lodge  between  the  flanges. 

Angle-iron  rings  are  frequently  used  in  French  and  English  boilers  for  securing  the 
furnaces  to  the  shell  and  to  the  back-connections.  In  all  cylindrical  boilers  constructed 


SEC.  7.  SHELL,  FURNACES,  AND  BACK-CONNECTIONS.  •  229 

for  United  States  naval  vessels  the  furnaces  are  riveted  to  flanges  turned  on  the  back 
tube-sheet  and  on  the  front-head  of  the  boiler,  double-riveting  being  used  at  the  front 
and  single-riveting  at  the  back  of  the  furnace. 

The  furnaces  of  the  boiler  illustrated  on  Plate  XV.  are  made  of  two  plates,  the  up- 
per one  £"  thick  and  the  bottom  one  -fa"  thick,  welded  together  6  inches  below  the 
centre  line.  The  plate  forming  the  furnace-crown  is  flanged  outward  at  the  back  and 
is  riveted  to  the  back  tube-sheet ;  the  bottom-plate  is  continued  straight  till  it  meets 
the  back-plate  of  the  back-connection,  being  riveted  to  the  flange  turned  on  the 
latter. 

Lloyd's  formula  for  the  collapsing  strength  of  circular  flues  is :  « 

89,600  x  square  of  thickness  of  plate  in  inches  __  j  working  pressure  in 

Length  of  flue  in  feet  X  outside  diameter  of  flue  in  inches  ~  (  pounds  per  sq.  inch. 

The  Surveyors  of  the  Board  of  Trade  (England)  determine  the  strength  of  circular 
furnaces  according  to  the  following  rule : 

"  Circular  furnaces  with  the  longitudinal  joints  welded  or  made  with  a  butt-strap : 

90,000  x  the  square  of  the  thickness  of  the  plate  in  inches 

(Length  in  feet  + 1)  x  diameter  in  inches  =  WOrkmS  Pressure  ^  **•  m" 

"Without  the  Board's  special  approval  of  the  plans  the  pressure  is  in  no  case  to 

,  8,000  X  thickness  in  inches     „„     , 

exceed  -       ,.          — : — =—  — .    The  length  to  be  measured  between  the  rings,  if 

diameter  m  inches 

the  furnace  is  made  with  rings. 

"  If  the  longitudinal  joints,  instead  of  being  butted,  are  lap-jointed  in  the  ordinary 
way,  then  70,000  is  to  be  used  instead  of  90,000,  excepting  only  when  the  lap  is  bevelled 
and  so  made  as  to  give  the  flues  the  form  of  a  true  circle,  when  80,000  may  be  used. 

"  When  the  material  or  the  workmanship  is  not  of  the  best  quality  the  constants 
given  above  must  be  reduced — that  is  to  say,  the  90,000  will  become  80,000,  the  80,000 
will  become  70,000,  the  70,000  will  become  60,000 ;  and  when  neither  the  material  nor 
the  workmanship  is  of  the  best  quality  such  constants  will  require  to  be  further  re- 
duced, according  to  circumstances  and  the  judgment  of  the  surveyor,  as  in  the  case  of 
old  boilers. 

"  One  of  the  conditions  of  best  workmanship  must  be  that  the  joints  are  either 
double-riveted  with  single  butt-straps  or  single-riveted  with  double  butt-straps,  and  the 
holes  drilled  after  the  bending  is  done  and  when  in  place,  and  afterwards  taken  apart, 
the  burr  on  the  holes  taken  off,  and  the  holes  slightly  countersunk  from  the  outside." 

7.  Combustion-chambers  and  Back-connections. — In  the  usual  type  of  loco- 


230  STEAM  BOILERS.  CHAP.  IX. 

motive  boilers  (see  Plates  IV.  and  V.)  the  front  tube-sheet  forms  the  back  of  the  fur- 
nace ;  in  other  instances  (see  Plate  III.)  the  gases  enter  a  separate  combustion-chamber 
on  leaving  the  furnace  ;  and  in  the  usual  type  of  return-tube  boilers  the  back-connection 
serves  as  a  combustion-chamber. 

The  opening  leading  from  the  furnace  to  the  combustion-chamber  is  contracted  to 
the  smallest  area  that  will  give  the  required  draught  by  the  bridge  which  at  the  same 
time  serves  as  a  support  for  the  back  of  the  grate.  Plates  VI.,  VII.,  XVII.  illus- 
trate the  usual  manner  of  forming  the  bridge-wall  in  rectangular  boilers  of  United  States 
naval  vessels.  In  cylindrical  marine  boilers,  where  the  simplest  forms  and  unstayed 
surfaces  are  used  as  much  as  possible,  the  bridge  is  generally  formed  by  a  casting  lined 
with  fire-brick  above  the  surface  of  the  grate.  Figure  1,  Plate  III.,  illustrates  a  fre- 
quent mode  of  forming  the  bridge — viz.,  by  means  of  a  hollow  wall  communicating  with 
the  water-space  of  the  boiler ;  this  is  called  a  water -bridge.  The  top  of  a  water-bridge 
should  always  slope  or  curve  upwards  towards  the  ends  to  admit  of  the  rapid  escape  of 
steam-bubbles.  Sometimes  a  water-bridge  projects  downward  for  the  purpose  of  de- 
flecting the  flame  ;  it  is  then  called  a  hanging-bridge. 

Return-tubular  boilers  are  built  either  with  one  back-connection  common  to  all  the 
furnaces  or  with  a  separate  back-connection  for  each  furnace.  The  former  plan  simpli- 
fies the  construction  and  lessens  greatly  the  weight  of  the  boiler,  including  water  ;  and 
since  it  admits  of  placing  at  least  one  additional  row  of  tubes  over  each  furnace,  the 
heating-surface  is  about  the  same  as  when  each  furnace  has  a  separate  back-connection. 
The  principal  advantages  of  the  latter  plan  are  twofold — viz.,  first,  the  products  of  com- 
bustion are  kept  separate  till  they  enter  the  front-connection  or  uptake,  consequently 
the  efficiency  of  any  furnace  is  not  affected  by  counter-currents,  or  currents  of  cold  air 
entering  the  back-connection  through  adjoining  furnaces ;  secondly,  the  water-spaces 
between  the  separate  back-connections  and  nests  of  tubes  are  of  great  utility  in 
facilitating  the  circulation  of  the  water  in  the  boiler.  When  more  than  two  fur- 
naces are  contained  in  the  same  shell  separate  back-connections  are  generally  used. 
Cylindrical  boilers  calculated  to  bear  a  high  pressure  of  steam  are  often  made  with 
one  common  back-connection,  in  order  to  reduce  the  amount  of  flat  stayed  surface 
as  much  as  possible ;  when  they  contain  more  than  two  furnaces  it  would  be  diffi- 
cult to  get  plates  of  sufficient  size  for  a  single  back  tube-sheet  and  to  flange  the  sheet 
properly. 

In  the  horizontal-tubular  boiler  the  front  of  the  back-connection  is  formed  by  the 
back  tube-sheet,  which  in  the  cylindrical  boiler  consists  of  one  plate.  In  the  rectangu- 
lar boiler  it  generally  extends  down  to  the  straight  sides  of  the  furnace.  A  flange 


SEC.  8.  SHELL,  FURNACES,  AND  BACK-CONNECTIONS.  231 

encircling  the  furnace  is  turned  on  the  tube-sheet ;  the  top  and  sides  of  the  same  are 
likewise  flanged  for  riveting  it  to  the  top  and  side  plates  of  the  back-connection. 

In  the  vertical  return-tube  boiler  the  bottom  tube-sheet  is  connected  with  the  fur- 
nace by  a  separate  flanged  piece  (see  Plates  VI.,  VII.)  The  top  of  the  back-connection 
is  often  formed  by  curving  the  back-plate  to  a  large  radius ;  in  other  cases  the  back- 
plate  is  made  to  slope  inward,  thereby  increasing  the  width  of  the  water-space  at  the 
back  of  the  boiler,  and  allowing  the  steam-bubbles  to  escape  from  the  plate  readily  as 
soon  as  formed.  It  is  necessary  to  leave  sufficient  room  at  the  top  of  the  back-connec- 
tion for  calking  the  seams  and  expanding  the  tubes. 

8.  Systems  of  Boiler-building. — The  preliminary  tests  applied  to  boiler-plates 
to  determine  their  strength,  soundness,  and  quality,  methods  of  developing  the  lines 
of  curved  sheets  and  laying  out  the  flanges  and  rivet-holes,  and  the  various  opera- 
tions of  bending,  flanging,  welding,  shearing,  punching,  drilling,  riveting,  and  calking, 
have  been  described  and  discussed  in  chapters  v.  and  viii. 

Various  systems  are  followed  by  boiler-makers  in  building  boilers,  as  far  as  the 
laying-off,  the  fitting,  and  the  order  in  which  the  several  parts  are  riveted  together  are 
concerned.  Since  in  bending,  flanging,  and  forming  the  plates  absolute  accuracy  in 
accordance  with  prescribed  dimensions  is  impracticable,  and  since  slight  changes  in  the 
location  of  laps  and  seams  often  encroach  upon  the  available  space  in  such  a  manner  as 
to  make  other  modifications  absolutely  necessary,  it  is  important  to  verify  all  work  by 
fitting  the  plates  together  after  they  are  bent  and  flanged,  securing  them  temporarily 
by  bolts,  placing  the  various  parts  of  the  boiler  in  position,  and  thus  to  make  sure 
before  riveting  the  joints  permanently  that  this  can  be  done  without  straining  any  part 
unduly,  and  that  the  proper  clearance  is  maintained  between  the  several  parts.  Care 
must  be  had  to  join  the  parts  together  in  such  order  as  to  have  all  seams  accessible  for 
riveting  and  calking. 

The  rivet -holes  in  the  shell  of  rectangular  boilers  are  generally  punched  or  drilled  at 
first  in  one  plate  only,  which  then  serves  as  a  template  for  marking  the  corresponding 
holes  on  the  other  plate  while  it  is  temporarily  fitted  and  secured  in  position.  The 
rivet-holes  of  the  circumferential  and  longitudinal  seams  of  cylindrical  shells  and  of 
their  butt-straps  are  often  all  laid  off  and  punched  or  drilled  before  the  plates  are  bent ; 
this  work  can  be  done  more  accurately,  however,  when  the  holes  of  each  seam  are 
formed  in  one  plate  only,  which  then  serves  as  a  template  for  drilling  the  correspond- 
ing holes  in  the  other  plates  while  secured  in  position,  as  described  in  section  6  of 
chapter  viii. 

In  building  the  boiler  represented  on  Plate  XII.  the  two  rings  forming  the  cylindri- 


232  STEAM  BOILERS.  CHAP.  IX. 

cal  shell  are  fitted  and  secured  together  with  their  butt-straps  by  tack-bolts.  The 
back-head,  having  been  flanged  in  the  meanwhile,  is  then  fitted  in  place,  and  the  rivet- 
holes  on  the  circumferential  flange  are  marked  and  drilled.  The  back-head  having 
been  fitted  and  secured  again  to  the  back-section  of  the  shell,  the  longitudinal  butt- 
strap  of  the  latter  and  the  transverse  seam  of  the  back-head  are  riveted,  and  the  back- 
head  is  riveted  to  the  shell.  The  circumferential  butt-strap  is  riveted  to  the  back- 
section,  while  the  front-section  is  fitted  and  secured  to  it ;  the  longitudinal  and 
circumferential  seams  of  the  front-section  are  then  likewise  riveted.  After  this  the 
laps  are  calked  from  the  inside,  and  the  gusset  and  stay  plates  are  fitted  and  bolted  to 
the  back-head.  In  the  meanwhile  the  furnace-flues  have  been  constructed,  the  diffe- 
rent sections  having  been  riveted  together  and  calked  ;  the  front  and  back  tube-sheets 
have  been  flanged  and  drilled,  and  are  being  fitted  to  the  furnace-flues.  In  doing  this 
the  tube-sheets  are  kept  the  proper  distance  apart  and  parallel  with  each  other  by  a 
couple  of  wooden  struts  and  some  long  bolts  passing  through  the  tube-holes ;  a  few 
tubes  are  put  through  the  holes  to  make  sure  that  the  corresponding  holes  in  the  two 
plates  come  fair  with  each  other ;  thus  secured,  the  furnaces  and  tube-sheets  are  fitted 
in  the  boiler-shell.  The  holes  in  the  flanges  joining  the  tube-sheets  to  the  furnaces  and 
the  front-head  to  the  shell  are  marked  and  drilled.  The  furnaces  having  been  removed 
from  the  shell,  they  are  riveted  to  the  back  tube-sheet,  and  the  flanges  encircling  the 
furnaces  are  calked.  The  plates  forming  the  back-connection  are  fitted  to  the  back 
tube-sheet,  and  the  furnaces  and  back-connection,  temporarily  connected  by  bolts,  are 
fitted  in  the  shell.  The  rivet-holes  of  the  seams  of  the  back-connection  are  then 
marked  and  drilled,  the  plates  are  riveted  in  place,  and  such  joints  as  would  not  be 
accessible  afterward  are  calked  as  soon  as  riveted.  The  furnaces  and  back-connections 
are  now  placed  in  position  in  the  shell ;  the  front-head  is  fitted  and  riveted  to  the  fur- 
naces and  to  the  shell ;  the  stay  and  gusset  plates  are  riveted  to  the  heads  and  back- 
connections  ;  the  stay-bolts  and  other  braces  are  put  in  place  and  secured.  The  tubes 
are  then  put  in  and  expanded,  and  finally  all  remaining  seams  are  calked. 

In  building  rectangular  boilers  the  bottom  and  the  lower  part  of  the  sides  and  back 
are  fitted  and  riveted  while  the  furnaces  and  back-connections  are  being  constructed  ; 
these  are  then  put  in  position  in  the  shell  on  blocks  or  wedges ;  the  front,  as  far  as  the 
front-connection,  is  fitted  and  riveted,  the  holes  for  stays  are  marked  and  drilled,  and 
the  furnaces  are  permanently  secured  within  the  shell  by  stay-bolts,  and  the  crow-feet 
for  the  attachment  of  the  braces  are  riveted  to  the  furnace-crowns.  The  plates  forming 
the  back,  sides,  and  top  are  in  the  meanwhile  fitted  and  riveted  on,  generally  one  sheet 
at  a  time. 


SEC.  8.  SHELL,  FURNACES,  AND  BACK-CONNECTIONS.  233 

The  tube-boxes  of  the  vertical-tubular  boiler  represented  on  Plates  VI.  and  VII. 
are  fitted,  riveted,  and  calked  ;  the  lugs  and  straps  for  the  attachment  of  the  braces  are 
riveted  to  them,  and,  when  the  sides  of  adjoining  boxes  are  tied  together  by  lugs  and 
pins  instead  of  stay-rivets,  the  tubes  are  put  in  and  expanded  before  the  boxes  are  put 
into  the  boiler. 

The  front-connection  and  uptake  are  then  built  in,  and,  before  the  boiler  is  finally 
closed,  the  angle-irons  and  long  braces,  dry-pipes,  surface  blow-pipes,  and  everything 
which  could  not  afterwards  be  introduced  through  manholes  are  passed  into  the  boiler. 
The  braces  having  been  connected,  the  tubes  are  put  in  and  expanded,  and  all  the  re- 
maining seams  of  the  boiler  are  calked  inside  and  outside. 


CHAPTER  X. 

STAYS  AND   BRACES. 

1.  Systems  of  Bracing. — Bracing  has  to  be  applied  to  all  surfaces  of  a  boiler 
which  are  liable  to  alteration  of  form  under  pressure.  The  only  figures  which  require 
no  bracing  when  subjected  to  an  internal  pressure  are  the  cylinder  and  the  sphere. 
Mathematical  formulae  expressing  the  resistance  of  cylindrical  and  spherical  forms  to  a 
bursting  pressure  have  been  developed  in  sections  1  and  2,  chapter  vi. ;  and  in  section  3 
of  the  same  chapter  the  resistance  of  cylindrical  flues  to  an  external  collapsing  pressure 
has  been  investigated. 

Surfaces  are  stayed,  -first,  by  contrivances  which  make  them  self-supporting,  or 
transmit  the  strain  due  to  the  pressure  on  them  to  well-supported  places  lying  in  the 
same  plane.  To  this  class  belong  the  girder-stays  used  on  locomotive  fire-boxes  and  on 
the  flat  top  of  the  back-connections  of  many  marine  boilers  (see  Plates  IV.,  V.,  XV.) ; 
the  angle-irons,  T-irons,  and  spherical  strengthening-domes  sometimes  used  on  flat  sur- 
faces of  small  extent  (see  Plate  XII.) ;  likewise  the  various  devices  for  strengthening 
furnace-flues  described  in  section  6  of  chapter  ix. 

Secondly,  by  tying  them  to  other  surfaces  lying  in  different  planes  and  experiencing 
an  equal  amount  and  kind  of  stress  in  an  opposite  direction,  or  possessing  sufficient 
stiffness  to  prevent  alteration  of  form.  The  latter  method  is  the  one  most  usually  em- 
ployed ;  stay-bolts,  rod-braces,  direct  or  oblique,  branch-braces,  stay-tubes,  and  gusset- 
plates  are  used  for  this  purpose.  These  two  methods  are  also  frequently  used  in 
combination,  as  when  angle  or  T-irons  or  stay-plates  are  used  to  distribute  the  strain 
of  braces  over  a  larger  area  of  the  stayed  surface. 

There  are  several  advantages  in  favor  of  diminishing  the  number  of  braces  and  in- 
creasing their  sectional  area  correspondingly — viz.,  the  boiler  is  made  more  accessible 
and  the  circulation  of  the  water  is  less  obstructed  ;  it  is  easier  to  give  an  equal  tension 
to  the  fewer  braces  ;  larger  braces  are  relatively  less  reduced  in  sectional  area  by  an 
equal  rate  of  corrosion  than  smaller  ones.  When,  however,  the  spacing  of  the  braces 
exceeds  a  certain  limit,  depending  on  the  steam-pressure  and  the  thickness  of  the  plate, 
the  latter  bulges  excessively  between  the  stays,  and,  even  if  rupture  does  not  take  place, 


SEC.  1.  STAYS  AND  BRACES  235 

leaks  occur  around  the  stays  ;  to  prevent  this  action  the  plates  have  to  be  stiffened  in 
such  cases  by  T  or  angle  irons  or  by  an  additional  thickness  of  plate. 

Various  devices  in  bracing  are  employed  to  keep  the  interior  of  the  boiler  accessible 
as  much  as  possible  :  the  braces  are  made  so  that  they  can  be  easily  removed  and  re- 
placed ;  they  are  spaced  as  wide  apart  as  practicable  ;  surfaces  are  strengthened  by  self- 
supporting  devices,  or  diagonal  braces  and  gusset-plates  are  used  to  tie  adjoining  sides 
together,  leaving  the  space  midway  between  the  ends  of  the  boiler  unobstructed.  In 
order  to  obstruct  the  interior  of  the  boiler  as  little  as  possible  without  leaving  too  long 
an  interval  between  the  attachment  of  the  braces,  two  or  more  short  oblique  braces  are 
attached  to  one  main-brace  ;  the  connection  of  these  branches  with  one  another  and  with 
the  main-brace  is  made  either  by  a  flexible  joint  or  by  welding.  These  branch-braces 
are  also  called  "half -moon"  braces  from  the  form  sometimes  given  to  the  branches. 

Careful  attention  must  be  paid  to  see  that  the  parts  to  which  the  braces  supporting 
a  surface  are  attached  are  strong  enough  and  sufficiently  stayed  to  bear  the  strain 
thrown  on  them.  Difficulties  may  be  encountered  in  this  respect  when  a  larger  surface 
is  tied  to  a  smaller  one.  When  a  surface  is  tied  to  a  self-supporting  cylindrical  surface 
the  strain  on  the  latter  will  no  longer  be  uniformly  distributed  around  its  circumference, 
and  distortion  will  take  place  unless  the  cylindrical  plate  possesses  a  surplus  of 
stiffness. 

In  cylindrical  marine  boilers  the  cylindrical  shell  is  self-supporting ;  the  flat  ends 
and  the  back-connections  have  to  be  supported  by  bracing ;  the  methods  used  to  secure 
flues  against  collapse  have  been  described  in  the  last  chapter.  Above  the  back-connec- 
tions the  flat  ends  are  either  tied  directly  together  by  braces  extending  through  the 
whole  length  of  the  boiler,  or  are  secured  to  the  adjoining  portions  of  the  shell  by 
oblique  braces  or  giisset-plates.  The  lower  parts  of  the  flat  ends  are  tied  to  the  back- 
connections.  The  back-head  is  secured  to  the  latter  by  stay-bolts  ;  the  tube-sheets  are 
held  by  the  tubes,  and  for  further  security  special  stay-tubes  or  rod-braces  are  often 
added.  The  furnace-flues  serve  to  tie  the  lower  part  of  the  front-head  to  the  back-con- 
nection, and  any  portions  of  these  parts  remaining  unsupported  are  either  tied  together 
by  rod-braces  or  are  strengthened  by  gussets,  angle-irons,  stay-domes,  or  similar  de- 
vices. The  sides  and  bottom  of  the  back-connections  are  secured  against  collapse  by 
tying  them  with  stay-bolts  to  the  circular  shell  or  to  opposite  flat  sides.  The  top  of  the 
back-connections  is  generally  supported  either  by  girder-stays  or  by  gusset-plates 
secured  to  the  back-head. 

Plates  XVII. ,  X VIII.  illustrate  the  system  of  bracing  used  in  rectangular  boilers  of 
United  States  naval  vessels.  These  boilers  are  designed  to  carry  from  35  to  40  pounds 


236 


STEAM  BOILE&S. 


CHAP.  X. 


Fig.  103. 


of  steam,  and  the  shell  is  made  of  ^-inch  or  f-inch  iron.  Opposite  portions  of  the  flat 
bottom  and  sides  of  the  furnaces  and  connections  and  of  the  lower  part  of  the  shell  are 
tied  to  one  another  by  socket-bolts  spaced  from  7f  to  9  inches  apart. 
The  tube-sheets  are  sufficiently  stayed  by  the  tubes.  The  upper  por- 
tions of  the  ends  and  of  the  back  and  front  of  the  shell  are  tied  together 
by  a  system  of  parallel  horizontal  branch-braces  traversing  the  length  and 
breadth  of  the  boiler.  In  the  horizontal  return-tube  boiler  the  top  of 
the  shell  is  tied  directly  to  the  arched  furnace-crown,  the  braces  passing 
between  the  nests  of  tubes ;  but  in  the  boiler  having  vertical  tubes  the 
braces  of  the  top  are  attached  to  the  sides  of  the  tube-boxes,  and  these 
are  tied  to  the  furnace-crowns.  The  tendency  of  these  braces  to  distort  the  circular 
furnace-crown  is  counteracted  by  a  system  of  horizontal  stays,  secured  near  the  point 
of  attachment  of  the  braces  to  opposite  portions  of  each  pair  of  adjacent  furnaces.  The 
braces  are  connected  with  the  shell  of  the  boiler  by  means  of  T-irons,  generally  4"  X  3^" 
X  I",  spaced  from  12  to  14  inches  apart  from  centre  to  centre,  and  securely  riveted  to  the 
shell.  These  T-irons  run  in  continuous  lengths  as  far  down  the  sides  of  the  boiler  as  is 

Fig.  104.  Fig.  105. 


necessary  for  the  attachment  of  the  braces.  Lugs,  called  "  crow-feet,'"  are  riveted  to  the 
furnace-crowns  and  to  the  top  of  the  back-connections  for  the  attachment  of  the  braces 
by  means  of  a  bolt  passing  through  the  eye  (see  Plate  XVIII.)  Similar  lugs  are  riveted 


SEC.  2. 


STAYS  AND  BRACES. 


237 


Fig.  106, 


to  the  top  and  bottom  of  the  sides  of  the  vertical  tube-boxes  of  the  boiler  illustrated  on 
Plate  VI. 

In  many  English  horizontal  return-tube  boilers  the  lower  ends  of  the  braces  sup- 
porting the  flat  top  are  attached  in  the  manner  shown  in  figure  95.  By  the  direct 
attachment  of  the  braces  to  the  bottom  of  the  boiler  the  arched  furnace-crown  is  kept 
free  from  unnecessary  bracing  ;  but  the  cleaning  of  the  boiler  through  the  handholes  is 
rendered  difficult.  This  defect  is  remedied  by  attaching  these  braces  in  the  manner 
shown  in  figure  103,  a  method  used  principally  in  dry-bottom  boilers. 

In  order  to  dispense  with  the  braces  which  are  attached  to  the  centre  of  the 
furnace-crown  it  has  been  proposed  to  subdivide  each  branch  of  the  braces  sup- 
porting the  top  of  rectangular  boilers  in  the  manner  shown  in  figure  104;  and  in 
the  horizontal  return-tube  boilers  of  the  U.  S.  S.  Tippecanoe  (built  in  the  year  1864) 
the  system  of  bracing  shown  in  figure  105  was  applied.  The  main-brace  passes  be- 
tween the  nests  of  tubes  and  is  tied  to  the  sides  of  the  furnaces.  But  ordinarily  it  will 
not  be  found  advantageous  to  complicate  the  construction 
of  the  braces  by  such  devices,  since  very  accurate  fitting 
is  required  in  order  to  ensure  equal  tension  on  all  the 
branches. 

Figure  106  shows  a  system  of  bracing  applied  to  rectan- 
gular boilers  of  French  naval  vessels.  The  top  of  the  shell 
is  tied  by  oblique  braces  to  the  back  and  front  of  the  shell 
and  to  the  uptake.  N"o  braces  are  attached  to  the  arched 
furnace-crowns,  and  few  braces  have  to  be  removed  to 
make  the  upper  part  of  the  boiler  quite  accessible ;  but 
the  greatly-inclined  oblique  braces  and  their  attachments 
experience  a  great  strain,  and  the  top  and  sides  of  the 
boiler  would  possess  much  greater  stiffness  if  the  angle- 
irons  were  made  in  continuous  lengths. 

2.  Rules  for  Proportioning  Braces. — In  calculating  the  strength  of  braces  it 
is  generally  assumed,  when  the  plates  are  thin  relatively  to  the  pressure  of  steam 
carried  in  the  boiler,  that  each  brace  has  to  bear  the  whole  strain  due  to  the  total 
pressure  on  the  portion  of  the  surface  which  it  supports.  When  the  thickness  of  the 
plate  is  increased,  or  when  the  plate  is  otherwise  stiffened,  the  resistance  which  it 
offers  to  bending  may  be  taken  into  account  in  proportioning  the  dimensions  of  the 
braces. 

When  the  braces  are  spaced  evenly  in  parallel  and  perpendicular  rows  the  portion 


238  STEAM  BOILERS.  CHAP.  X. 

of  surface  supported  by  each  brace  is  represented  by  the  rectangles  into  which  the 
whole  surface  is  divided  by  the  rows  of  braces. 

A  large  factor  of  safety,  ranging  from  eight  to  sixteen,  is  used  in  calculating  the 
strength  of  braces  on  account  of  the  constant  diminution  of  their  sectional  area  by  cor- 
rosion, the  uncertain  strength  of  welded  parts,  and  the  impossibility  of  ensuring  an 
equal  tension  on  all  braces  under  the  varying  conditions  of  pressure  and  temperature. 

The  corrosion  of  braces  takes  place  most  rapidly  at  or  near  the  water-level,  where 
the  mechanical  action  of  the  water  in  washing  from  side  to  side,  and  the  alternate  wet- 
ting and  drying  of  the  braces,  cause  the  layers  of  oxide  and  scale  to  fall  off,  thus  ex- 
posing new  surfaces  to  corrosion.  The  stay-bolts  of  water-bottoms  corrode  rapidly  be- 
cause dirt  accumulates  there,  which  absorbs  and  retains  moisture  and  often  contains 
corrosive  substances.  It  is  also  found  that  braces  in  the  path  of  steam  flowing  to  stop- 
valves,  etc.,  suffer  greatly  from  decay,  and  that  braces  are  more  easily  attacked  at  welds 
than  at  points  where  the  fibres  of  the  rolled  bar  have  remained  undisturbed.  It  is  re- 
commended to  protect  braces  by  thin  washes  of  Portland  cement,  or  by  wrapping  them 
with  marline  or  canvas  and  white  or  red  lead,  and  with  galvanized  iron  wire.  Rods  of 
circular  section  are  evidently  less  affected  by  corrosion  than  square  or  flat  bars  and 
gusset  or  stay  plates,  since  they  expose  less  surface  in  proportion  to  their  sectional 
area. 

'  Lloyd's  Register  of  British  and  Foreign  Shipping'  contains  the  following  "  Rules 
for  Determining  the  Working  Pressure  in  New  Boilers": 

"Stays. — The  stays  supporting  the  flat  surfaces  are  not  to  be  subjected  to  a  greater 
strain  than  6,000  Ibs.  per  square  inch  of  section  if  of  iron,  and  8,000  Ibs.  if  of  steel,  cal- 
culated from  the  weakest  part  of  the  stay  or  fastening,  and  no  steel  stays  are  to  be 
welded. 

"  Flat  Plates. — The  strength  of  flat  plates  supported  by  stays  to  be  taken  from  the 
following  formula : 

C  X  T* 
— — —  =  working  pressure  in  Ibs.  per  square  inch,     [I.] 

where  T=  thickness  of  plate  in  sixteenths  of  an  inch  ; 
P  =  greatest  pitch  in  inches  ; 
C  =  90  for  plates  -ft  thick  and  below,  fitted  with  screw- stays  with  riveted 

heads ; 

C  =  100  for  plates  above  -ft-,  fitted  with  screw-stays  with  riveted  heads  ; 
C  =  110  for  plates  -ft  thick  and  under,  fitted  with  screw-stays  and  nuts  ; 
C  —  120  for  plates  above  -ft,  fitted  with  screw-stays  and  nuts  ; 


SBC.  2.  STAYS  AND  BRACES.  239 

C  =  140  for  plates  fitted  with  stays  with  double  nuts  ; 

C  =100  for  plates  fitted  with  stays  with  double  nuts,  and  washers,  at  least  £ 
thickness  of  plates  and  a  diameter  of  £  of  the  pitch,  riveted  to  the 
plates. 

"NOTE. — In  the  case  of  front-plates  of  boilers  in  the  steam-space  these  numbers 
should  be  reduced  20  per  cent.,  unless  the  plates  are  guarded  from  the  direct  action 
of  the  heat." 

The  rules  of  the  Board  of  Trade   (English)  limit  to  5,000  Ibs.  the  pressure  per 
,.  effective  square  inch  of  area  of  stay,  but  allow  a  greater  pressure  when  the  flat  surface 
is  stiffened  by  T-irons  or  angle-irons  in  an  approved  manner. 

The  same  authority  prescribes  the  following  rules  for  determining  the  highest  ad- 
missible steam-pressure  in  boilers  under  their  supervision,  according  to  the  manner  in 
which  the  stays  are  spaced  and  secured,  viz. : 

"  The  pressure  on  plates  forming  flat  surfaces  will  be  easily  found  by  the  following 
formula,  which  is  used  in  the  Board  of  Trade : 

"~g  —  1  ^  =  working  Pressure-     C11-] 

T=  thickness  of  plate  in  sixteenths  of  an  inch  ; 

S  —  surface  supported  in  square  inches  ; 

C  =  constant  according  to  the  following  circumstances : 

C  =  100  when  the  plates  are  not  exposed  to  the  impact  of  heat  or  flame,  and 
the  stays  are  fitted  with  nuts  and  washers,  the  latter  being  at  least 
three  times  the  diameter  of  the  stay  and  two-thirds  the  thickness  of 
the  plates  they  cover ; 

C  =  90  when  the  plates  are  not  exposed  to  the  impact  of  heat  or  flame,  and 
the  stays  are  fitted  with  nuts  only  ; 

C  =  60  when  the  plates  are  exposed  to  the  impact  of  heat  or  flame,  and  steam 
in  contact  with  the  plates,  and  the  stays  fitted  with  nuts  and  washers, 
the  latter  being  at  least  three  times  the  diameter  of  the  stay  and  two- 
thirds  the  thickness  of  the  plate  they  cover ; 

C  =  54  when  the  plates  are  exposed  to  the  impact  of  heat  or  flame,  and  steam 
in  contact  with  the  plate,  and  the  stays  fitted  with  nuts  only  ; 

C  =  80  when  the  plates  are  exposed  to  the  impact  of  heat  or  flame,  with 
water  in  contact  with  the  plates  and  the  stays  screwed  into  the  plate 
and  fitted  with  nuts  ; 


240  STEAM  BOILERS.  CHAP.  X. 

C  —  60  when  the  plates  are  exposed  to  the  impact  of  heat  or  flame,  with 
water  in  contact  with  the  plate,  and  the  stays  screwed  into  the  plate, 
having  the  ends  riveted  over  to  form  a  substantial  head  ; 
C  =  36  when  the  plates  are  exposed  to  the  impact  of  heat  or  flame,  and  steam 
in  contact  with  the  plates,  with  the  stays  screwed  into  the  plate  and 
having  the  ends  riveted  over  to  form  a  substantial  head. 

"  When  the  riveted  ends  of  screwed  stays  are  much  worn,  or  when  the  nuts  are 
burned,  the  constants  should  be  reduced  ;  but  the  surveyor  must  act  according  to  the 
circumstances  that  present  themselves  at  the  time  of  survey,  and  it  is  expected  that  in 
cases  where  the  riveted  ends  of  screwed  stays  in  the  combustion-boxes  and  furnaces  are 
found  in  this  state  it  will  be  often  necessary  to  reduce  the  constant  60  to  about  36." 

The  foregoing  rules  of  Lloyd's  and  of  the  Board  of  Trade  are  modifications  of  for- 
mula [IX.],  section  5,  chapter  vi.,  representing  the  strength  of  flat  square  plates  secured 
at  the  edges,  viz.  : 


.       n 

£  =  —  -y  --  or  p  —  — 
2       k  n 

In  using  this  formula  for  calculating  the  thickness  of  flat  plates  supported  by  stay- 
bolts  Weisbach  substitutes  for  n  the  diagonal  of  the  square  formed  by  four  adjacent 
stay-bolts.  Since  this  diagonal  is  equal  to  n  V  2  we  have  the  equation  : 


k 


[III.] 


With  the  dimensions  usually  employed  in  practice  plates  supported  by  stay-bolts  do 
not  give  way  by  rupture  in  the  middle  between  the  rows  of  stays,  but  by  buckling  and 
stretching,  thereby  breaking  off  the  riveted  heads  of  the  stays  in  the  first  place  and 
then  pulling  the  stay  through  the  enlarged  hole,  or  by  tearing  through  the  holes.  It 
must  be  remembered  that  when  a  single  stay  gives  way  the  area  of  the  unsupported 
surface  between  the  adjoining  stays  is  increased  four  times. 

Neglecting  the  stiffness  of  the  plate,  the  following  equation  must  exist  between  the 
strength  of  the  stay-bolts  and  that  of  the  supported  flat  plate,  when  d  is  the  diameter  of 
the  stay-bolt,  and  when  the  tensile  strength  and  the  factor  of  safety  of  the  stay-bolts  and 
of  the  plate  are  supposed  to  be  the  same,  viz.  : 

n'p=2  k  V  —  .7854  d?  k  ;  hence 
d  =  1.8t    [IV.] 


SEC.  2.  STAYS  AND  BRACES.  241 

In  practice,  to  allow  for  corrosion  and  give  greater  holding  power  to  the  riveted 
heads,  the  diameter  of  stay  -rivets  is  seldom  made  less  than  twice  the  thickness  of  the 
plate. 

Rules  for  proportioning  and  for  finding  the  strength  of  screw  stay-bolts  with  riveted 
ends  or  nuts,  as  deduced  from  a  series  of  experiments,  will  be  found  in  section  9  of  the 
present  chapter. 

The  tension  of  gussets  must  be  calculated  by  the  same  rule  as  that  for  oblique  stay- 
bars  ;  but  a  much  larger  factor  of  safety  must  be  employed  in  the  case  of  gussets,  not 
only  because  they  expose  relatively  much  more  surface  to  corrosion,  but  because  the 
resultant  tension  of  a  gusset  is  concentrated  near  one  edge.  Rankine  says  :  "It  ap- 
pears advisable  that  its  sectional  area  should  be  three  or  four  times  that  of  a  stay-bar 
for  sustaining  the  pressure  on  the  same  area." 

In  the  girder-stay  the  plate  acts  as  a  bottom  flange  to  the  girder  and  is  fixed  at  the 
ends,  while  the  bar  forms  the  web  and  upper  flange  and  is  merely  supported  at  both 
ends.  We  may  consider  the  stay  as  a  rectangular  beam  supported  at  both  ends  and 
loaded  in  the  middle  or  at  several  points,  according  to  the  number  of  bolts  sup- 
porting the  plate.  When  loaded  in  the  middle  its  strength  is  determined  by  formula 

^Z  =  *|^[V.],  where 

p  =  pressure  of  steam  in  pounds  per  square  inch  ; 

S=  area  of  plate  supported  in  square  inches  ; 

I  =  length  of  span  of  stay-bar  in  inches  ; 

b  —  breadth  of  stay  -bar  in  inches  ; 

d  =  depth  of  stay-bar  in  inches  ; 

Jc  —  coefficient  of  resistance  equal  to  about  50,000  Ibs.  per  square  inch. 
A  small  factor  of  safety,  about  four,  may  be  used  in  calculating  the  dimensions  of  the 
stay-bar  from  the  foregoing  formula,  on  account  of  the  strength  imparted  by  the  plate 
acting  as  the  bottom  flange  of  the  girder.  Calling  the  distance  between  two  adjoining 
girders  from  centre  to  centre  D,  and  taking  four  as  the  factor  of  safety,  we  get  for  the 
depth  of  the  girder-bar,  from  the  above  formula,  the  expression  : 


The  breadtn  of  girder  -stays  varies  generally  from  one-third  to  one-fifth  of  the  depth. 
In  v,Tought-iron  bars  having  a  depth  of  not  less  than  one-tenth  of  their  length  the  de- 
flection due  to  a  load,  less  than  that  required  to  overcome  the  limit,  of  elasticity,  is 


242      '  STEAM  BOILERS.  CHAP.  X. 

trifling.  The  deflection  varies  directly  as  the  load  and  the  cube  of  the  length,  and  in- 
versely as  the  breadth  and  the  cube  of  the  depth. 

The  Board  of  Trade  (English)  prescribes  the  following  rule  for  determining  the 
highest  pressure  of  steam  admissible  in  boilers  having  surfaces  stayed  by  girder- 
stays,  viz. : 

"  When  the  tops  of  combustion-boxes  or  other  parts  of  a  boiler  are  supported  by 
solid  rectangular  girders  the  following  formula,  which  is  used  in  the  Board  of  Trade, 
will  be  useful  for  finding  .the  working  pressure  to  be  allowed  on  the  girders,  assuming 
that  they  are  not  subjected  to  a  greater  temperature  than  the  ordinary  heat  of  steam, 
and,  in  the  case  of  combustion-chambers,  that  the  ends  are  fitted  to  the  edges  of  the 
tube-plate  and  the  back  plate  of  the  combustion-box  : 

(W-P)I)XL  =  workinS  Pressure-     IT11-] 
W  =  width  of  combustion-box  in  inches  ; 
P  =  pitch  of  supporting-bolts  in  inches  ; 

D  =  distance  between  the  girders  from  centre  to  centre  in  inches  ; 
L  =  length  of  girder  in  feet ; 
d  =  depth  of  girder  in  inches  ; 
T '=  thickness  of  girder  in  inches  ; 

C  =  500  when  the  girder  is  fitted  with  one  supporting-bolt ; 
C  —  750  when  the  girder  is  fitted  with  two  or  three  supporting-bolts  ; 
C  =  850  when  the  girder  is  fitted  with  four  supporting-bolts. 

"The  working  pressure  for  the  supporting-bolts,  and  for  the  plate  between  them, 
shall  be  determined  by  the  rule  for  ordinary  stays." 

Lloyd's  Eegister  prescribes  the  same  rule  in  a  slightly  different  form. 
The  shearing  strength  of  bolts,  pins,  or  rivets  by  which  braces  are  connected  or  are 
attached  to  the  boiler  may  be  considered  equal  to  the  tensile  strength  of  the  brace  ;  for 
the  weakening  effect  of  welding  may  be  considered  as  offsetting  the  excess  of  tensile 
strength  over  shearing  strength  of  wrought-iron. 

"To  find  the  strength  of  an  easy -fitting  fastening  against  shearing,  multiply  the 
sectional  area  by  the  modulus  of  strength  ;  then  take  two-thirds  of  the  product  if  the 
fastening  is  rectangular  in  section,  or  three-quarters  if  it  is  circular  or  elliptical  in 
section. 

"  For  &  perfectly  tight-fitting  fastening  the  strength  is  the  whole  product  just  men- 
tioned. Many  actual  fastenings  are  intermediate  between  easy  and  perfectly  tight 
fastenings."  (Rankine.) 


SEC.  3.  STAYS  AND  BRACES.  243 

Experiments  on  the  strength  of  wronght-iron  bolts,  when  subjected  to  the  action  of 
single-shear  and  of  double-shear,  are  recorded  in  section  7  of  the  present  chapter. 

In  proportioning  the  ends  of  eye-bars  or  braces  connected  by  pins  or  bolts  the  bear- 
ing-surface of  the  latter  is  an  important  element  of  strength.  When  the  dimensions  of 
the  bolt  are  proportioned  so  as  to  make  its  sectional  area  equal  to  the  least  sectional 
area  of  the  bar,  but  with  insufficient  bearing-surface,  the  originally  round  hole  will  be- 
come pear-shaped  under  an  excessive  strain  ;  the  iron  around  the  hole  which  was  sub- 
jected to  compression  will  become  thickened,  and  the  other  portions  of  the  iron  around 
the  hole  which  were  subjected  to  tension  will  become  thinned,  and  fracture  will  ulti- 
mately commence  and  continue  at  this  thin  part  around  the  eye  regardless  of  the  width 
of  the  head.  Experiments  by  Charles  Fox  on  the  flat  links  of  the  chains  of  suspension- 
bridges  lead  him  to  the  conclusion  that  the  area  of  the  semi-cylindrical  bearing-surface 
should  be  a  little  more  than  equal  to  the  sectional  area  of  the  smallest  part  of  the  body, 
and,  as  the  iron  in  the  head  is  not  generally  as  strong  as  that  in  the  body,  the  sum  of 
the  width  of  the  iron  on  both  sides  of  the  hole  should  be  ten  per  cent,  greater  than  the 
width  of  the  body. 

In  boiler  braces  this  increased  area  of  bearing-surface  is  often  obtained  by  making 
the  depth  of  the  eye  greater  than  the  diameter  or  thickness  of  the  bar. 

Experiments  made  to  determine  the  proper  proportions  of  pins  and  eye-bars,  and 
the  best  method  of  forming  them,  will  be  found  in  section  8  of  the  present  chapter. 

3.  Screw-stays  and  Socket-bolts. — In  narrow  spaces,  as  at  the  sides  and  be- 
tween the  furnaces  and  in  the  water-legs  and  water-bottoms  of  rectangular  boilers,  at 
the  sides,  back,  and  bottom  of  the  back  and  front  connections,  and  between  the  tube- 
boxes  of  vertical  water-tube  boilers,  the  opposite  parallel  plates  are  tied  together  by 
stay-bolts,  of  which  two  varieties  maybe  distinguished — viz.,  screw-stays  and  socket- 
bolts.  The  former  are  screwed  into  both  plates,  and,  in  addition,  their  ends  are  gene- 
rally secured  by  a  riveted  head  or  by  a  nut ;  the  socket-bolts  pass  through  the  plates 
without  being  screwed,  being  held  either  by  a  riveted  head  or  by  a  nut,  and  derive  their 
name  from  the  thimble  or  socket  surrounding  them  and  fitted  between  the  plates.  Such 
stays  resist  a  collapsing  as  well  as  a  bursting  strain,  and  permit  the  riveting  to  be  per- 
formed and  the  nuts  to  be  set  up  hard  without  springing  the  plates.  Stay-bolts  should 
always  be  spaced,  when  possible,  in  vertical  and  horizontal  rows  in  large  surfaces,  as 
such  an  arrangement  facilitates  the  scaling  of  narrow  water-spaces.  It  is  necessary  that 
the  holes  in  the  two  plates  connected  by  stay-bolts  be  exactly  opposite  each  other,  and 
that  the  stays  stand  perpendicular  to  both  plates,  else  the  varying  lateral  strains  due  to 
differences  in  pressure  and  temperature  will  soon  cause  the  bolts  to  leak.  Stay-bolts 


244  STEAM  BOILERS.  CHAP.  X. 

generally  fail  in  consequence  of  the  excessive  bulging  of  the  plates,  which  causes  either 
the  heads  of  the  stays  to  break  or  the  plates  to  crack  through  the  holes ;  the  strength 
of  such  stays  is  therefore  greatly  increased  by  every  addition  to  the  depth  of  their 
heads  and  to  the  area  covered  by  them.  On  this  account  stay-bolts  secured  by  nuts  are 
much  stronger  than  riveted  stays ;  and  by  the  use  of  washers  the  strength  of  stayed 
surfaces  may  be  still  further  increased.  Stay-bolts  secured  by  nuts  have  the  additional 
advantage  that  they  may  be  renewed  in  many  places  where  rivets  could  not  well  be 
driven  without  moving  the  boiler  from  its  seat.  Nuts  should,  however,  not  be  used  on 
surfaces  in  direct  contact  with  the  fire  or  exposed  to  great  heat,  because  they  are  more 
liable  to  be  burnt  than  riveted  heads,  and  will  soon  give  trouble  by  leaking  ;  in  ashpits 
the  nuts  interfere  with  the  hauling  of  the  ashes  and  are  liable  to  be  loosened  by  the 
hoes,  unless  they  are  protected  by  a  false  ashpan. 

The  thimble  or  socket  of  socket-bolts  (see  Plate  XVIII.)  is  either  made  of  cast-iron 
or  of  a  piece  of  boiler-iron  bent  into  a  cylinder.  Its  length  should  be  exactly  equal  to 
the  width  of  the  space  between  the  stayed  plates.  They  are  put  in  position  by  hand  or 
with  tongs,  and  are  held  by  wooden  plugs  passing  through  them  and  both  plates  till 
the  stay-bolts  are  put  in.  Where  not  otherwise  accessible  the  sockets  are  wired  into 
place  by  reeving  a  wire  or  string  through  both  holes,  hooking  the  bight  between  the 
plates,  pulling  it  within  reach,  cutting  it,  passing  one  of  the  ends  .through  the  socket, 
fastening  the  cut  ends  together,  and  hauling  taut  on  the  other  ends  till  the  socket  is  in 
position.  When  stay-rivets  are  used  the  shank  of  the  stay  should  not  be  too  long  and 
should  fit  the  socket  well  when  hot,  else  in  riveting  the  shank  may  be  bent,  as  repre- 
sented  in  figure  107;  in  such  a  case,  when  pressure  is  applied,  the  rivet 
will  be  straightened,  the  plates  will  bulge,  and  leakage  will  ensue. 

Owing  to  the  absence  of  sockets  screw  stay-bolts  are  less  cumbersome 
and  obstruct  narrow  water-spaces  less  than  socket-bolts,  but  more  labor 
and  greater  accuracy  in  fitting  are  required  with  the  former.  The  screw- 
stays  should  fit  tight  in  both  plates.  Whenever  screw  stay-bolts  have  to 
be  replaced  it  will  be  found  necessary  to  ream  out  the  holes  and  cut  the  threads  anew. 
Hollow  screw  stay-bolts  have  been  used  to  admit  jets  of  air  to  the  furnace  and  combus- 
tion-chamber. 

For  plates  f  inch  thick  and  less  the  screw-stays  should  have  fourteen  threads  to  the 
inch  ;  for  J-inch  and  f-inch  plates  twelve  threads  to  the  inch  are  sufficient.  The  thread 
is  generally  cut  over  the  whole  length  of  the  bolt,  and  one  end  is  left  square  till  the 
stay  is  screwed  into  the  plates.  The  middle  of  the  shank  should  be  turned  down  to  the 
bottom  of  the  thread,  for  it  has  been  found  that  the  elasticity  of  bars  under  a  tensile 


SEC.  4 


STAYS  AND  BRACES. 


245 


strain  is  much  impaired  by  narrow  grooves  turned  in  them,  the  elongation  being  appa- 
rently confined  to  these  reduced  places.  Bolts  with  a  smooth  shank  seem  also  to  suffer 
less  from  corrosion  than  when  the  thread  is  continuous. 

The  holding  power  of  screw  stay-bolts  is  greatly  increased  by  securing  their  ends  by 
nuts  or  by  riveting  them  over.  A  very  soft  quality  of  iron  is  required  for  such  stays, 
in  order  that  this  cold-riveting  may  be  done  without  injuring  the  screw-threads  in  the 
plate,  and  that  the  riveted  head  may  possess  proper  strength.  A  description  of  the 
best  shape  and  dimensions  and  of  the  proper  manner  of  forming  the  riveted  heads  of 
screw  stay-bolts  will  be  found  in  section  9  of  the  present  chapter. 

4.  Various  Forms  of  Stays  and  Modes  of  fastening  them. — In  French  boilers 
the  stay  represented  in  figure  108  is  often  used  in  narrow  water-spaces ;  it  is  stiff  and 
efficient,  preventing  collapse  as  well  as  bursting,  but  its  use  involves  more  labor  than 
that  of  stay-bolts. 

The  vertical  sides  of  tube-boxes  and  back-connections  have  been  stayed  by  means  of 
lugs  or  pieces  of  angle-iron  riveted  to  the  opposite  surfaces  and  connected  by  pins  pass- 
ing through  corresponding  holes  (see  figure  109).  This  method  is  to  be  condemned,  for, 
even  when  these  lugs  are  accurately  fitted,  the  strain  on  the  pin  is  unequal ;  and  this 
action  is  aggravated  to  a  dangerous  extent  by  the  almost  unavoidable  inaccuracies  in 
the  location  of  these  lugs,  as  shown  in  figure  110.  A  less  objectionable  form  of  this 


Fig.  108. 


Fig.  109.  Fig<  110 


Fig.  111. 


tStSs. 


kind  of  stay,  which  was  applied  to  the  boilers  of  U.  S.  S.  Lancaster,  is  shown  in 
figure  111. 

For  short  stays,  connecting  surfaces  that  are  not  parallel — for  instance,  on  the  arched 
crowns  and  at  the  lower  rounded  corners  of  furnaces,  and  on  the  rounded  top  of  back- 
connections — a  flat  bar  with  the  ends  bent  to  the  required  angle,  and  secured  at  each  end 
by  a  single  rivet,  is  generally  used  (see  Plate  XVIII.)  The  foot  should  never  make  an 
acute  angle  with  the  body  of  this  stay,  else  there  will  be  difficulty  in  driving  the  rivet ; 
on  this  account  the  two  ends  often  have  to  be  bent  in  different  directions,  making  the 
stay  "]_-shaped.  Such  stays  have  the  fault  mentioned  in  connection  with  oblique  braces 


246  STEAM  BOILERS.  CHAP.  X. 

—viz.,  that  there  is  a  bending  strain  tending  to  spring  the  angle  which  the  body  of  the 
stay  forms  with  the  foot,  and  which  should  be  made,  on  that  account,  with  a  large  fillet. 
When  such  rigidly-fastened  braces  are  longer  it  is  better  to  make  the  ends  T-shaped,  as 
in  figure  108,  and  secure  them  by  two  rivets,  so  that  there  is  no  longer  a  bending  strain 
but  a  direct  pull  on  the  fastenings ;  sometimes  the  ends  of  the  brace  are  made  forked, 
as  in  figure  112,  the  two  branches  being  welded  to  the  main  body.  The  triangular 

brace  shown  in  figure  113,  used  to  tie  the  bot- 
I   '  torn  of  the  boiler  to  the  lower  rounded  corners 

112<   fl  °^  adjacent  furnaces,  is  very  stiff,  but  inter- 

feres with  the  cleaning  of  the  water -bottoms 
through  the  handholes. 

The  ends  of  braces  that  have  to  be  removed 

and  replaced  from  time  to  time  either  pass 

through  the  plates  and  are  secured  by  nuts  and  washers,  or  they  are  connected  by  pins 
or  bolts  with  lugs,  angle  or  T-irons  riveted  to  the  stayed  surfaces  inside  the  boiler.  The 
former  method  of  fastening  is  frequently  used  in  English  rectangular  boilers  for  secur- 
ing the  lower  ends  of  the  braces  which  tie  the  top  of.  the  boiler  to  the  bottom  or  to  the 
furnace-crown  and  back-connection.  Such  braces  are  generally  secured  by  a  nut  on 
both  sides  of  the  plate  (see  figure  95),  but  sometimes  a  shoulder  forged  on  the  brace 
takes  the  place  of  the  nut  inside  the  boiler.  The  large  nuts  and  washers  inside  the  fur- 
nace, exposed  to  an  intense  heat,  are  apt  to  give  much  trouble,  and  the  varying  lateral 
strains  to  which  these  long  braces  are  exposed  tend  not  only  to  cause  leaks  but  to  break 
off  the  ends  in  the  thread.  Rods  secured  by  nuts  and  washers  are  commonly  used  to 
stay  the  uptake  by  tying  it  to  the  surrounding  steam -drum. 

The  flat  ends  of  cylindrical  boilers  are  often  tied  together  by  cylindrical  rods  passing 
through  the  shell  and  secured  by  nuts  on  both  sides  of  the  plates,  the  ends  of  the  brace, 
as  far  as  the  thread  is  cut,  being  enlarged.  The  strain  due  to  the  tension  of  these  braces 
is  distributed  over  the  plates  either  by  large  washers  or  by  riveting  angle-irons  or  an 
extra  thickness  of  plate  to  them.  This  brace  is  simple  and  easily  adjusted,  and  with 
accurate  workmanship  all  lateral  strains  may  be  avoided  when  the  end  plates  are  suffi- 
ciently stiffened  so  that  they  do  not  buckle  to  an  appreciable  degree.  It  is,  however, 
inconvenient  to  remove  long  braces  by  pulling  them  out  of  the  boiler,  and  the  screw- 
threads  inside  the  boiler  become  soon  coated  with  rust  and  scale,  making  the  turning  of 
the  nuts  very  difficult.  On  this  account  a  different  fastening  was  applied  to  some  rod- 
braces  of  the  boilers  of  U.  S.  S.  Terror,  illustrated  on  Plate  IX.  The  brace  is  held  by 
bolts  screwed  into  the  enlarged  ends  from  outside  the  shell ;  the  ends  of  the  brace  bear 


SEC.  4. 


STAYS  AND  BRACES. 


247 


against  washers  which  can  be  driven  out  after  the  bolts  are  withdrawn,  and  the  brace 
can  then  be  removed  to  a  convenient  place  within  the  boiler.  In  the  boilers  of  U.  S.  S. 
AmphitrUe  (see  Plate  IX.)  the  ends  of  the  shell  are  stiffened  by  two  angle-irons  riveted 
to  them  a  small  distance  apart,  and  the  brace  is  drawn  up  by  nuts  against  a  cross-bar 
resting  on  these  angle-irons.  In  the  boilers  of  U.  S.  S.  Miantonomoh  (see  Plate  IX.) 
the  tap-bolt  passes  through  a  ferrule  against  which  the  brace  bears  ;  this  ferrule  is  to 
be  filled  with  red-lead,  and  is  intended  to  protect  the  bolt  against  scale  and  corrosion. 
Figure  114  illustrates  a  brace  used  to  stay  the  upper  portion  of  the  flat  ends  of  some 


Fig.  114. 


cylindrical  boilers  built  by  R.  Napier  &  Co.,  Glasgow,  in  1870.  The  ends  of  the  boilers 
are  stiffened  by  two  T-irons  (4$"  x  4£")  spaced  10  inches  between  centres  ;  bolts,  2  inches 
in  diameter  and  21  inches  long,  are  riveted  to  the  T-irons,  20  inches  apart ;  each  pair  of 
bolts  carries  a  stout  cross-bar  secured  by  nuts  ;  the  brace,  2J  inches  in  diameter,  passes 
through  the  middle  of  this  cross-bar,  the  ends  being  held  by  cotters  ;  the  brace  is  made 
in  two  parts,  connected  by  means  of  an  eye  and  pin.  This  brace  is  easily  removed  and 
adjusted  to  the  proper  tension,  but  the  work  involved  in  its  manufacture  makes  it 
rather  expensive. 

The  bracing  applied  to  the  boiler  on  Plate  XV.  is  much  used,  the  T-ends  being 
secured  to  the  angle-irons  either  by  rivets  or  bolts.  This  form  makes  a  very  stiff  brace, 
and  the  strain  is  well  distributed  over  the  stayed  plate  ;  consequently  the  braces  may 
be  spaced  rather  wide  apart,  but  it  is  difficult  to  remove  and  replace  such  heavy  braces 
within  the  boiler. 

The  attachment  of  a  brace  by  means  of  a  single  bolt  or  pin,  making  a  flexible  joint, 
has  the  great  advantage  that  it  allows  the  brace  to  adjust  itself  to  the  direction  of  the 
resultant  of  the  opposing  forces,  so  that  it  experiences  tension  only  in  the  direction  of 
its  axis ;  on  this  account  this  method  of  fastening  is  to  be  recommended,  especially 
when  the  braces  are  very  long  and  relatively  slender,  and  when  they  are  not  perpen- 
dicular to  the  stayed  surfaces.  When  such  braces  are  made  with  jaws  or  forked  ends, 
which  take  hold  of  the  lugs  or  T-irons  riveted  to  the  plate  (see  U.  S.  S.  Monadnock, 
Plate  IX.),  the  place  where  the  forked  end  joins  the  body  of  the  brace  is  apt  to  be  a 
weak  spot ;  a  simple  eye-bar  is  not  only  free  from  this  weakness,  but  is  cheaper  to 


248 


STEAM  BOILERS. 


CHAP.  X. 


make.  The  eye-bar  takes  hold  of  two  angle-irons  or  bracket-plates,  placed  far  enough 
apart  to  let  the  end  of  the  brace  pass  between  them  without  jamming ;  the  bracket- 
plates  are  often  made  of  considerable  depth,  and  are  stiffened  by  tying  each  pair  to- 
gether by  bolts  or  rivets,  using  thimbles  to  keep  them  the  proper  distance  apart.  The 
bracket-plates  are  made  of  the  form  shown  on  Plate  IX.,  to  make  them  lighter  and  to 
facilitate  the  removal  of  the  braces. 

The  brace  represented  in  figure  115  is  illustrated  in  plates  accompanying  Ledieu's 


Fig.  115. 


'  Traite  elementaire  des  Appareils  a  Vapeur  de  Navigation,'  and, 
although  not  commonly  applied,  may  sometimes  be  used  to  ad- 
vantage instead  of  branch-braces.  The  short  horizontal  link  re- 
sists the  normal  component  of  the  stress  on  the  braces. 

In  the  branch-brace  each  of  the  oblique  branches  is  sometimes 
formed  by  a  pair  of  separate  links  ;  usually,  however,  each  link 
consists  of  two  rigidly-connected  branches,  as  shown  on  Plate 
IX.  (U.  S.  S.  Terror}.  Two  links  are  used  in  order  to  avoid  forked 
ends.  These  links  have  been  formed  of  solid  plates,  an  example 
of  which  may  be  found  on  Plate  XVIII. ;  these  are  .very  stiff,  but  heavy  and  clumsy. 

Triangular  links  of  the  form  shown  in  figure  116  have  been  iised  to  connect  the  lower 
end  of  braces  to  the  arched  crowns  of  adjacent  furnaces.  The  horizontal  bar  experi- 
ences compression  and  prevents  distortion  of  the  furnace-crowns  ;  but  it  renders  access 
to  the  interior  over  the  furnaces  through  the  manholes  very  difficult,  and  it  is  therefore 
better  to  rivet  a  separate  stay  to  the  furnaces  a  little  lower  down,  as  shown  on 
Plate  XVIII. 

In  the  boilers  of  U.  S.  S.  Mohongo  a  similar  triangular  frame  was  riveted  to  the  fur- 
nace-crowns (see  figure  117),  making  the  boilers  almost  inaccessible  over  the  furnaces. 


Fig.  117. 


Frequently  the  oblique  branches  are  formed  by  simply  bending  a  bar  and  letting  the 
pin  of  the  brace  bear  directly  on  this  bar  at  the  angle ;  the  ends  of  the  bent  bar  are 


SBC.  5. 


STAYS  AND  BRACES. 


249 


either  made  with  an  eye,  for  the  purpose  of  attaching  them  by  means  of  a  pin,  or  they 
are  rigidly  riveted  to  the  boiler  (see  figure  118).  Such  braces  are  much  cheaper  and 
more  easily  made  than  those  illustrated  on  Plate  XVIII.,  but  they  experience  irregular 
bending  strains,  and  they  do  not  take  up  the  strain  on  the  stayed  plates  as  well,  and 
are  consequently  less  reliable  and  not  to  be  recommended. 

The  braces  should  be  connected  by  well-fitting  bolts  with  coarse  threads  secured  by 
nuts,  or  by  pins  secured  by  cotters  or  keys  ;  the  nut  or  key  does  not  merely  hold  the 
bolt  or  pin  in  place,  but,  when  drawn  up  tight,  adds  much  to  the  strength  of  the  joint 

Fig.  118. 

Fig.  119.  Fig.  120. 


by  preventing  the  jaws  from  spreading  or  the  displacement  of  the  links,  so  that  the  pin 
or  bolt  experiences  simply  a  shearing  stress  and  not  a  bending  stress.  The  use  of  split 
pins  (see  figure  119)  should  be  avoided,  since  they  rarely  fit  the  holes  as  well  as  bolts, 
and  give  little  or  no  lateral  stiffness  to  the  joint ;  besides,  the  split  ends  are  liable  to 
break  off  when  they  are  opened,  after  inserting  the  pin,  to  prevent  working  out,  or  closed 
for  the  purpose  of  backing  it  out. 

In  order  to  facilitate  the  adjustment  of  long  braces  to  the  proper  tension  the  connec- 
tion between  the  branches  and  the  brace  is  sometimes  made  in  the  manner  illustrated  in 
figure  120  ;  or  the  braces  are  made  in  halves,  connected  by  a  turnbuckle  made  of  brass 
so  that  it  does  not  rust  fast  to  the  brace.  (See  Plate  XVIII.) 

5.  Fitting  and  Adjusting  Rod-braces.— Welding  should  be  avoided  as  much  as 
possible  in  boiler-braces,  for  the  strength  of  the  brace  depends  upon  the  soundness  of 
the  weld,  which  is  frequently  an  uncertain  element,  and  the  iron  at  the  weld  is  much 
more  readily  attacked  by  corrosion  than  at  the  parts  where  the  fibre  has  remained  un- 
disturbed. 

The  ends  of  long  braces  have  to  be  forged  separately  to  the  required  shape ;  and 
after  being  fitted,  the  threads  cut,  the  pin-holes  bored,  etc.,  they  are  welded  to  the  rods. 
It  is  safer  to  forge  rod-braces  at  first  a  trifling  amount  too  long,  and  to  adjust  them  to 
the  exact  length  by  "upsetting"  the  rod.  "Drawing-down,"  even  to  a  small  extent, 
should  be  avoided ;  in  case  the  brace  is  found  to  be  too  short  the  rod  should  be  cut  and 
a  piece  welded  in. 


250 


STEAM  BOILERS. 


CHAP.  X. 


The  pin-holes  in  the  ends  of  braces  should  be  bored  accurately,  so  that  the  pins  fit 
well  and  are  thus  subject  to  a  shearing  stress  and  not  to  a  bending  stress.  In  ordinary 
boiler- work  the  pin-holes  are  often  not  bored  at  all,  but  are  made  by  bending  a  square 
bar  so  as  to  form  a  loop,  and  welding  the  ends  together.  Figure  121  illustrates  a  com- 
mon method  of  forming  the  forked  end  of  a  brace  which  takes  hold  of  a  T-iron  or  a 
single  "crow-foot." 

The  vertical  braces  that  pass  between  the  rows  of  horizontal  tubes  are  often  made  of 


Fig. 121. 


taken  into  account. 


Fig.  122.  flat  bars  in  order  to  save  room.  When  the  manner  of  attaching 
the  brace  to  the  shell  would  place  its  longer  side  in  a  transverse 
direction  to  the  axes  of  the  tubes  a  half -twist  is  given  to  the  end 
of  the  brace,  as  shown  in  figure  122.  Sufficient  clearance  must  be 
allowed  between  the  braces  and  the  tubes  so  that  under  the  vary- 
ing strains  the  braces  do  not  chafe  against  the  tubes  and  cut  them 
through.  In  long,  horizontal  braces  the  "sagging"  has  to  be 
In  the  rectangular  boiler  the  long,  horizontal  braces  tying  the  ends 
of  the  boiler  together  are  placed  slightly  above  the  plane  of  the  shorter,  stiffer  braces 
which  tie  the  front  and  back  of  the  boiler  together,  and  rest  on  these  ;  in  other  cases 
long,  horizontal  braces  are  supported  in  the  middle  by  light  hooks  suspended  from 
the  T-irons  above. 

Braces  should  be  set  up  before  the  tubes  are  expanded  and  before  the  external  seams 
of  the  shell  are  calked.  Before  setting  up  the  braces  of  the  large  flat  surfaces  of  rect- 
angular boilers  it  is  well  to  shore  these  up  evenly,  else  there  is  danger  of  setting  up  the 
braces  near  the  middle  of  the  surface  more  than  those  near  the  sides,  thus  giving  to  the 
surface  a  " dished"  form. 

To  test  whether  long  braces  are  set  up  to  the  same  tension,  tap  each  brace  at  the 
same  distance  from  the  support  with  a  hammer,  and  note  whether  the  sound  is  in  the 
same  key — the  tauter  brace  vibrates  quicker  and  gives  a  note  of  higher  key  than  the 
slacker  one,  provided  the  rods  have  the  same  diameter  and  length. 

6.  Girder-stays,  Gusset-stays,  Stay-plates,  Stay-domes,  etc. — Girder-stays 
are  either  forged  solid  (see  Plate  IX.)  or  they  are  made  of  two  plates  riveted  together  at 
the  ends,  with  distance-pieces  between  them  and  a  square  washer  placed  on  top  for 
the  bolt  to  bear  against  (see  figure  123).  A  clear  space  of  about  1£  inches  should  be 
kept  between  the  girder-stay  and  the  supported  plate  ;  to  prevent  the  buckling  of  the 
plate  in  screwing  up  the  bolts  tight,  ferrules  surrounding  the  bolts  are  inserted  between 
the  plate  and  the  bar,  or  the  bolts  pass  through  short  projections  forged  on  the  lower 
side  of  the  bar.  The  girder  should  be  of  such  length  that  its  ends  rest  OH  the  perpen- 


.-.  0. 


STAYS  AND  BRACES. 


251 


Fig.  123. 


dicular  plates  forming  the  sides  or  ends  of  the  back-connection  or  fire-box,  and  not  on 
the  supported  plate.  The  girder-stays  of  locomotive  fire-boxes  extend  sometimes 
through  the  whole  width  of  the  boiler,  the  ends 
being  riveted  or  bolted  to  the  shell.  Heavy 
T-irons  are  also  used  for  girder-stays,  and 
when  they  are  long  they  are  supported  in  one 
or  several  places  by  braces  hung  from  the  top 
of  the  shell ;  the  stay-bolts  are  placed  stagger- 
ing, passing  alternately  through  either  flange 
of  the  T-iron. 

The  front  plate  of  the  back-connection  of 
the  boiler  illustrated  on  Plates  VIII.  and  IX. 
is  stayed  by  a  contrivance  which  may  be  classed  among  the  girder-stays ;  the  plate  is 
supported  by  a  bolt  passing  through  a  wrought-iron  frame  with  four  branches,  which 
rest  on  the  plate  at  places  well  supported  by  the  furnace-flues  and  the  sides  of  the  back- 
connection. 

Flat  surfaces  of  small  area  are  sufficiently  stiffened  by  angle  or  T-irons  riveted  to 
them,  without  the  use  of  braces.  The  flat  ends  of  cylindrical  sheUs  have  been  stiffened 
in  the  same  manner,  but  when  their  diameter  is  large  an  awkward  strain  is  thrown  on 
the  rivets  attaching  the  heads  to  the  cylindrical  shell ;  in  such  cases  it  is  better  to  use 
gusset-plates.  These  should  be  secured  by  double  flanges  formed  either  by  riveting 
two  angle-irons  to  the  plate  or  by  turning  one  flange  on  the  plate  and  riveting  an  angle- 


iron  to  the  other  side  ;  the  rivets  attaching  the  two  flanges  to  the  shell  should  be  spaced 
staggering.     It  is  advantageous  to  extend  the  length  of  the  gusset  along  the  shell,  and 


252  STEAM  BOILERS.  CHAP.  X. 

secure  it  also  to  the  second  belt  of  plates,  and  not  to  the  first  only,  although  the  latter  is 
the  usual  practice. 

The  gussets  which  tie  the  heads  to  the  cylindrical  shell  of  a  boiler  are  often  arranged 
radially,  so  that  the  flanges  attaching  the  gussets  to  the  shell  may  all  be  bent  to  a  sight 
angle  ;  but  when  the  continuation  of  the  gussets  on  the  flat  ends  forms  stay-plates  for 
the  attachment  of  braces  (see  Plate  XII.)  it  is  preferable  to  place  them  parallel  to  each 
other. 

Where  gussets  or  stay -plates  are  attached  to  heating-surfaces,  as  to  the  top  of  back- 
connections,  portions  of  the  flanges  between  the  rivets  are  cut  away,  as  in  figure  124,  or 
the  plates  are  held  by  lugs  riveted  to  them  (see  figure  125) ;  a  better  plan  is  shown  on 
Plate  VIII.,  where  thimbles  surrounding  the  rivets,  and  at  least  one  inch  long,  are  placed 
between  the  flanges  of  the  angle-irons  and  the  stayed  plate  ;  the  rivets  are  spaced  stag- 
gering, passing  alternately  through  either  of  the  two  flanges. 

The  stay -domes  which  strengthen  the  front  plate  of  the  back-connection  of  the  boiler 
shown  on  Plate  XII.  were  formed  by  pressing  the  heated  plate  into  a  mould,  using  a 
spherical  shot  of  suitable  diameter  as  a  die,  the  ends  of  the  plate  being  held  by  clamps 
so  as  to  form  a  flat  flange.  These  domes  were  riveted  over  circular  openings  cut  in  the 
plate  of  the  back-connection.  The  furnace-tubes  and  side  plates  of  the  back-connection 
give  sufficient  stiffness  to  the  plate  to  support  the  thrust  on  the  flange  of  the  stay- 
dome. 

7.  Experiments  on  the  Shearing  Strength  of  Wrought-iron  Bolts. — Ex- 
periments on  shearing  wrought-iron  bolts,  conducted  at  the  Washington  Navy- Yard 
in  1868,  by  Chief  Engineer  William  H.  Shock,  U.S.N.,  gave  the  results  recorded  on 
Plate  XX.,  where  the  shearing  attachments  for  single  and  double  shear  are  like- 
wise illustrated.  The  Rodman  testing-machine  was  used  in  making  these  experi- 
ments. 

The  bolts  were  of  good  American  commercial  iron,  not  turned.  Five  sizes  of  bolts 
were  tested,  their  diameters  being  |",  f ",  f",  f  ",  and  1" ;  six  specimens  of  each  size  were 
subjected  to  the  single-shear  test,  and  the  same  number  to  the  double-shear  test.  The 
bolts  fitted  snugly  in  the  respective  holes  of  the  shearing  attachments,  but  the  latter 
were  made  slightly  oval,  the  larger  diameter  lying  in  the  direction  in  which  the 
stress  was  applied.  The  nuts  on  the  bolts  were  set  up  close,  but  not  hard,  so  as  to 
prevent  lateral  motion  of  the  two  parts  of  the  shearing  attachment  without  producing 
friction. 

The  smaller  bolts  showed,  on  the  whole,  a  larger  shearing  strength  per  square  inch 
of  sectional  area  than  the  larger  bolts ;  but  the  decrease  in  strength  was  not  regular  or 


SBC.  8.  STAYS  AND  BRACES.  253 

uniform.     The  increase  of  average  strength  per  square  inch  of  sectional  area  of  the  bolts 
for  double-shear  over  that  of  single-shear  was,  for  the 

f-inch  bolts,  86.2  per  cent, 
f-inch  bolts,  97.0  per  cent, 
f-inch  bolts,  101.1  per  cent, 
f-inch  bolts,  82.6  per  cent. 
1-inch  bolts,  85.0  per  cent. 

Average  for  all  sizes  of  bolts,  90.2  per  cent. 

In  experiments  No.  20  and  21  of  the  double-shear  test  the  nuts  were  not  screwed 
up  close,  and  the  results  show  a  remarkable  decrease  of  strength  in  comparison  with 
the  four  other  bolts  of  the  same  diameter  subjected  to  double-shear.  In  experiment 
No.  20  this  decrease  of  strength  amounted  to  9.1  per  cent,  of  the  average  result  given 
by  the  four  other  bolts,  and  to  7.1  per  cent,  of  the  least  result  given  by  the  bolts  of 
the  same  series  ;  and  in  experiment  No.  21  this  decrease  of  strength  amounted  to  13.8 
per  cent,  and  11.9  per  cent,  respectively. 

8.  Experiments  made  to  determine  the  proper  Dimensions  of  Pins,  Eyes, 
and  Shanks  of  Boiler-braces. — In  the  course  of  the  years  1878-79  experiments  were 
conducted  at  the  Navy- Yard,  Washington,  D.  C.,  under  the  direction  of  the  Bureau  of 
Steam-Engineering,  by  a  board  consisting  of  Chief  Engineer  Jas.  P.  Sprague,  U.S.N., 
and  Passed  Assistant  Engineer  George  E.  Tower,  U.S.N.,  the  object  being  to  ascertain 
the  proper  proportions  for  the  ends  of  boiler-braces.  The  Rodman  testing-machine 
represented  on  Plate  I.  was  used  in  making  these  experiments. 

The  test-specimens  were  made  in  the  form  of  eye-bars,  which  were  secured  by  accu- 
rately-fitted iron  or  steel  pins  to  jaws  attached  to  the  testing-machine,  so  that  the  pins 
were  subjected  to  double-shear.  The  proportions  of  the  eye-bars  in  each  series  of  expe- 
riments were  gradually  changed  till  the  metal  at  the  sides  and  at  the  crown  of  the  hole 
and  in  the  shank  of  the  brace  appeared  to  be  very  nearly  equally  strained  when  rup- 
ture took  place. 

In  the  first  series  of  experiments  the  specimens  were  made  of  flat  iron  bars  $•  inch 
thick  and  from  1^  to  1J  inches  wide.  The  eyes  were  formed  by  drawing  out  the  bar 
under  the  hammer,  bending  and  welding  it  around  a  mandrel  £  inch  less  in  diameter 
than  the  finished  hole,  then  reaming  out  the  hole  to  fit  the  pin ;  the  rest  being  finished 
to  the  proper  size  in  a  shaping-machine.  The  surfaces  were  planed  and  finished,  and 
careful  examination  did  not  reveal  any  defect  in  the  welding.  -Nevertheless  three  of 
the  fifteen  specimens  broke  in  the  weld,  and  some  of  the  eyes  made  from  the  same  bar 


254 


STEAM  BOILERS. 


CHAP.  X. 


broke  at  greatly  different  strains,  indicating  that  the  iron  had  been  injured  somewhat 
in  welding.     The  depth  of  the  eye  was  in  every  case  equal  to  the  thickness  of  the  bar. 

The  following  proportions  are  submitted  by  the  board,  "as  those  which  will  give 
nearly  a  uniform  strength  in  the  eye,  slightly  in  excess  of  that  of  the  shank,  suppos- 
ing the  weld  to  be  perfect  and  the  quality  not  to  be  materially  affected  in  welding 
and  working ;  these  proportions  will  apply  until  the  thickness  of  the  bar  is  equal  to 
its  breadth ;  with  a  steel  pin  of  proper  tensile  strength  its  diameter  can  be  reduced  to 
65  per  cent,  of  the  breadth  of  the  bar,  with  the  same  results,"  (see  figure  126 :) 


Fig.  126. 


Breadth  of  shank  of  iron  bar  =          x 

Diameter  of  iron  pin  =  .917  x 

Width  of  metal  on  each  side  of  eye  =  .600  x 
Width  of  metal  at  crown  of  eye  =  .600  x 
Depth  of  eye  equal  to  thickness  of  bar. 

In  the  second  series  of  experiments  the  eyes  were  cut  from  flat  bars,  f  inch  thick 
and  2f  inches  wide,  witJiout  forging.  The  specimens  were  planed  smooth  on  both 
sides  to  bring  them  to  the  proper  thickness.  The  holes  were  drilled  and  reamed  to  fit 
the  pins  accurately.  The  specimens  were  then  put  on  mandrels  and  cut  out  to  the  re- 
quired form  in  the  shaping-machine. 

The  following  proportions  are  submitted  by  the  board  for  eye-bars  made  in  this  man- 
Fig.  127. 


i 


ner,  as  approximating  as  nearly  as  possible  to  a  uniform  strength  in  all  parts,  the  depth 
of  the  eye  being  equal  to  the  thickness  of  the  bar.    These  proportions  will  apply  until 


SEC.  9.  STAYS  AND  BRACES.  255 

the  thickness  of  the  bar  is  equal  to  its  breadth.    With  a  steel  pin  the  diameter  can  be 
reduced  to  66  per  cent,  of  the  breadth  of  the  bar.     (See  figure  127.) 

Breadth  of  shank  of  iron  bar  =          x 

Diameter  of  iron  pin  =  .917  x 

Width  of  metal  on  each  side  of  eye  =  .665  x 
Width  of  metal  at  crown  of  eye  =  .722  x 
Depth  of  eye  equal  to  thickness  of  bar. 

A  third  series  of  experiments  was  made  with  specimens  cut  from  flat  bars  and  hav- 
ing similar  dimensions  as  the  specimens  tested  in  the  second  series  of  experiments,  but 
with  iron  or  steel  pins  of  increased  diameters.  The  result  showed  that,  by  using  iron 
and  steel  pins  having  the  respective  proportions  deduced  from  the  first  and  second 
series  of  experiments,  the  conditions  of  strain  on  the  eye-bars  are  not  materially 
altered. 

A  fourth  series  of  experiments  was  made  with  eye-bars  made  of  round  iron  slightly 
larger  than  the  required  size.  "The  eye  was  formed  (solid)  by  upsetting  the  end  of  the 
bar  and  forging  to  the  required  shape ;  the  eye  and  bar  were  brought  as  nearly  as  pos- 
sible to  given  dimensions  in  the  lathe  and  planer.  The  hole  in  the  eye  was  drilled,  and 
the  pin  made  to  fit  easily  but  not  loose." 

The  following  proportions  are  recommended  by  the  Board  for  eye-bars  formed  in 
this  manner,  the  depth  of  the  eye  being  equal  to  the  diameter  of  the  bar : 

Area  of  cross-section  of  shank  of  round  iron  bar     =       if 
Area  of  cross-section  of  iron  pin  y* 

Area  of  cross-section  of  metal  on  each  side  of  eye  =  .74  y* 
Area  of  cross-section  of  metal  at  crown  of  eye         =  .90  y* 

(See  '•Report  on  Experiments  to  ascertain  Proportions  for  the  Ends  of  Boiler-braces.' 
Washington,  D.  C.,  November  24,  1879.) 

9.  Experiments  on  Screw  Stay-bolts. — For  the  purpose  of  determining  the 
strength  and  holding  power  of  screw  stay-bolts  for  boilers  under  different  conditions, 
experiments  were  conducted  at  the  Navy-Yard,  Washington,  D.  C.,  in  the  course  of  the 
year  1879,  under  the  direction  of  the  Bureau  of  Steam-Engineering,  by  a  board  consist- 
ing of  Chief  Engineer  James  P.  Sprague,  U.S.N.,  and  Passed  Assistant  Engineer  George 
E.  Tower,  U.S.N. 

These  experiments  were  of  two  kinds. 

In  the  first  place  a  series  of  tests  was  made  "  to  determine  the  comparative  force 
necessary  to  pull  screw  stay-bolts  of  iron  and  copper  through  iron,  low-steel,  and  cop- 


256  STEAM  BOILERS.  CHAP.  X 

• 

per  boiler-plates."  The  Rodman  testing-machine  illustrated  on  Plate  I.  was  used  in 
making  these  tests. 

"  Three  trials  each  were  first  made  with  £"  iron  plates  and  1"  iron  stay-bolts,  not 
riveted,  and  riveted  over  with  the  ordinary  thin  or  low  conical  head,  simply  arranged  so  as 
to  show  the  actual  strength  to  resist  pulling  through  the  plate,  the  .supports  consisting 
of  heavy  plates  with  a  hole  If"  in  diameter ;  the  boiler-plate  resting  upon  the  heavy 
plate  and  the  stay-bolt  adjusted  to  the  centre  of  the  hole,  thus  allowing  the  bolt  to 
have  a  clear  space  around  it  equal  to  the  overlapping  of  the  riveted  head  on  the  boiler- 
plate. The  bolts  not  riveted  drew  out  at  an  average  strain  of  32,785  pounds ;  those 
riveted  with  the  low  conical  head,  made  according  to  general  practice  by  leaving  three 
threads  through  to  form  the  head,  required  an  average  strain  of  35,033  pounds  to  draw 
them  through  the  plate  ;  the  rivet-head  giving  an  additional  strength  of  2,248  pounds  in 
a  1"  stay-bolt. 

"  In  testing  those  with  low  conical  heads  it  was  observed  that  the  bulging  of  the  plates 
caused  the  lap  of  the  rivet-head  on  the  plate  to  commence  giving  way  or  break  off 
some  time  before  the  maximum  strain  was  reached,  thus  leaving  more  for  the  threads 
on  the  bolts  to  sustain.  As  the  strain  and  bulge  of  the  plates  increased,  the  plate 
around  the  bolt  turned  downward  and  outward  until  the  threads  in  the  plate  almost  en- 
tirely cleared  those  on  the  bolts,  so  that  in  almost  every  case  there  were  only  from  one 
to  two  threads  stripped  or  injured  on  the  bolt  when  it  drew  out ;  therefore  it  was 
deemed  advisable  to  form  the  head  in  a  different  manner,  and,  after  several  experi- 
ments, it  was  decided  that  the  rivet- head  should  be  made  as  follows  :  First,  by  leaving 
as  much  of  the  bolt  through  the  plate  as  could  be  riveted  over  without  injury  to  the 
iron,  which  was,  in  case  of  the  excellent  iron  being  used,  equal  in  length  to  about  one- 
half  the  diameter  of  the  bolt.  This  was  riveted  over  in  the  following  manner :  A  few 
quick,  sharp  blows  were  struck  on  the  end,  slightly  upsetting  the  iron ;  the  head  was 
then  formed  to  shape  with  a  button-head  set  made  to  a  spherical  segment. 

"  It  was  found  that  this  could  be  done  in  nearly  the  same  time  as  that  used  in  riveting 
the  ordinary  low  conical  stay-bolt  heads  at  the  Washington  yard,  and  with  much  less 
injury  to  the  iron  ;  also,  that  it  only  required  one  riveter  and  a  helper,  whereas  by  the 
old  method  two  riveters  were  used. 

"Three  trials  each  were  then  made  with  £"  iron  plates  and  1"  iron  stay-bolts:  not 
riveted ;  riveted  with  ordinary  low  conical  head,  with  three  threads  left  through  for 
riveting ;  riveted  with  button-head,  a  little  over  five  threads  left  through  for  riveting ; 
and  with  button-head,  the  size  of  stay-bolt  being  increased  to  li". 

"Each  end  of  the  stay-bolt  was  secured,  in  the  manner  specified,  in  the  centre  of  a 


SBC.  9.  STAYS  AND  BRACES.  257 

square  plate,  which  was  supported  by  four  bolts,  one  in  each  corner,  by  means  of  which 
it  was  held  in  the  testing-machine.  These  supporting-bolts  were  placed,  in  different 
experiments,  four  and  five  inches  apart  from  centre  to  centre,  equally  distant  from  the 
stay-bolt. 

"  The  average  ultimate  strain  required  to  pull  the  above  bolts  through  the  i*  plate 
was  as  follows : 

WITH  SUPPORTS  4*  FROM  CENTRE  TO  CENTRE. 

Pounds. 

Y  bolt,  not  riveted 21,970 

1"  bolt,  ordinary  low  conical  head,  three  threads  left  through  for  riveting 25,147 

\"  bolt,  button-head  ;  length  of  bolt  left  through  for  riveting  equal  to  VV  diameter 

of  bolt 33,791 

li*  bolt,  button-head ;  length  left  through  for  riveting  equal  to  £  diameter  of 

bolt 38,885 

WITH  SUPPORTS  5*  FROM  CENTRE  TO  CENTRE. 

1"  bolt,  ordinary  low  conical  head 22,137 

1"  bolt,  button-head ;  length  left  through  for  riveting  equal  to  ft  diameter  of 

bolt 31,282 

If  bolt,  button-head ;  length  left  through  for  riveting  equal  to  i  diameter  of 

bolt 35,812 

"The  great  increase  of  holding  power  given  to  screw  stay-bolts  by  forming  the 
riveted  head  with  a  button-head  set  being  demonstrated  by  these  tests,  further  experi- 
ments were  made  with  iron,  steel,  and  copper  plates  and  stay-bolts  secured  in  the  same 
manner,  for  the  purpose  of  determining  the  best  proportions  of  diameter  of  stay-bolts 
to  thickness  of  plate  under  different  conditions 

-"  In  comparing  the  results  of  three  different  thicknesses  in  each  case  (f,  f,  i* 
plate)  of  iron  plates  and  iron  bolts,  steel  plates  and  iron  bolts,  steel  plates  and  steel 
bolts,  the  diameter  of  the  bolts  being  1",  li",  and  If,  their  distance  apart  and  condi- 
tions of  trial  being  the  same,  it  was  found  that  in  the  case  of  the  iron  plates  and  iron 
bolts  the  strain  required  to  draw  the  bolts  through  the  plates  was  equal  to  74.77  per 
cent,  of  the  tensile  strength  of  the  bolt,  with  the  steel  plates  and  iron  bolts  77.36  per 
cent.,  and  with  the  steel  plate  and  steel  bolts  85.42  per  cent." 

In  the  next  series  of  experiments  the  plates  and  stay-bolts  were  arranged  so  as  to 
represent  a  portion  of  the  wall  of  a  fire-box,  and  water-pressure  was  used  to  produce 
the  strain. 


258  STEAM  BOILERS.  CHAP.  X. 

Iron,  steel,  and  copper  plates  were  used,  varying  from  J  inch  to  \  inch  in  thickness. 
The  iron  and  steel  screw  stay-bolts  were  spaced  from  4  inches  to  8  inches  apart,  and, 
after  being  screwed  through  the  plates,  their  ends  were  secured  either  by  riveting  them 
over  with  a  button-head  set  or  by  means  of  nuts  and  washers. 

The  Board  conclude  their  report  on  these  experiments  with  the  following  recommen- 
dations, viz. : 

"  After  a  careful  examination  of  the  results  of  these  experiments  in  particular  we 
are  satisfied  that  the  following  formulae  will  correctly  and  safely  represent  the  working 
strength  of  good  material  in  flat  surfaces,  supported  by  screw  stay-bolts  with  riveted 
button-shaped  heads  or  with  nuts,  when  the  thickness  of  the  plates  forming  said  sur- 
faces and  the  screw  stay-bolts  are  made  in  accordance  with  the  dimensions  and  con- 
ditions given  in  Table  Y.  W  —  safe  working  pressure ;  T  —  thickness  of  plate ; 
d  —  distance  from  centre  to  centre  of  stay-bolt : 

rjrt 

For  iron  plates  and  iron  bolts W  —  24,000  -™- 

rjn 

For  low-steel  plates  and  iron  bolts W  —  25,000  -~- 

yn 

For  low-steel  plates  and  low-steel  bolts W=  28,000  -  ~- 

yn 

For  iron  plates  and  iron  bolts,  with  nuts W  —  40,000  -^ 

JTJ 

For  copper  plates  and  iron  bolts W '  —  14,500  -^ 

"  To  obtain  the  ultimate  bursting  pressure  multiply  the  results  of  the  above  formulae 
by  8,  which  is  the  factor  of  safety  iised. 

"  The  rivet-heads  to  be  a  segment  of  a  sphere,  formed  by  first  upsetting  the  end  of 
the  bolt  with  a  few  quick,  sharp  blows  of  the  hammer,  then  finished  to  shape  with  the 
hammer  and  button-head  set.  Where  nuts  can  be  used  instead  of  riveted  heads  they 
should  be  of  the  standard  size,  suited  to  the  diameter  of  the  bolt,  faced  on  the  side 
bearing  on  the  plate,  and  dished  out  so  as  to  form  an  annular  bearing-surface  of  as 
large  a  diameter  as  the  nut  will  allow,  and  of  a  breadth  and  depth  given  in  the  table. 
Before  securing  the  nut  in  place  the  dished  portion  should  be  filled  with  red-lead  putty 
made  stiff  with  fine  iron  borings." 


SEC.  9. 


STAYS  AND  BKACES. 


259 


TABLE  Y. 

DIMENSIONS  AND  CONDITIONS  FOR  MAKING  IRON  AND  LOW-STEEL  SCREW  STAY-BOLTS  FOR  FLAT 
SURFACES  SUBJECT  TO  INTERNAL  PRESSURE  FOR  DISTANCES  RANGING  FROM  FOUR  TO  EIGHT 
INCHES  (INCLUSIVE)  FROM  CENTRE  TO  CENTRE  OF  STAY-BOLTS. 


Thickness  of 
plate. 

Diameter  of 
bolt  outside  of 
thread. 

Number  of 
threads  per 
inch. 

Length  of  bolt 
left  through  for 
riveting  in 
fractions  of 
diameter 
of  bolt. 

Height  of 
rivet-head 
when 
finished. 

Diameter  of 
base  of  rivet- 
head  not  to 
exceed  when 
finished 

Nuts. 

Breadth  of 
annular 
bearing-surface. 

Dished  out  to 
a  depth  of 

i" 

i" 

u 

i 

TV" 

ITV" 

TV" 

TV" 

i" 

if 

J4 

i 

i" 

«*" 

i" 

TV" 

}" 

if" 

12 

i 

TV" 

if" 

TV" 

A" 

i" 

if" 

12 

i 

i" 

4" 

i" 

A" 

CHAPTER  XI. 

FLUES  AND  TUBES. 

1.  Flue-boilers. — The  flues  or  channels  for  the  passage  of  the  products  of  combus- 
tion from  the  furnace  to  the  chimney  were  at  first  made  very  large  in  marine  boilers,  so 
as  to  give  easy  access  for  cleaning  and  repairs,  and,  in  order  to  get  a  great  amount  of 
heating-surface,  these  passages  were  often  made  very  tortuous.  While  the  pressures 
of  steam  used  in  marine  boilers  exceeded  but  little  the  atmospheric  pressure  the  flues 
were  frequently  made  with  flat  sides  (see  figure  1,  Plate  XXI.) ;  but  with  increased 
steam-pressures  flues  of  a  circular  cross-section  have  come  into  general  use.  The  longi- 
tudinal seams  of  these  flues  are  either  lap-welded  or  riveted.  Stationary  flue-boilers 
are  frequently  made  very  long,  with  one  or  two  large  circular  or  elliptical  flues  running 
through  the  whole  length  of  the  boiler.  The  length  of  marine  boilers  being  limited  by 
the  available  space,  the  required  amount  of  heating-surface  is  obtained  in  them  by 
using  return-flues,  and  by  decreasing  their  diameter  and  increasing  their  number  (see 
figure  2,  Plate  XXI.) 

In  the  drop-flue  boiler  (see  figure  3,  Plate  XXI.)  the  products  of  combustion  pursue 
a  downward  course  in  their  passage  from  the  furnace  to  the  chimney  ;  by  this  arrange- 
ment the  cooler  gases  are  brought  in  contact  with  surfaces  surrounded  by  the  less 
heated  water  at  the  bottom  of  the  boiler,  and  consequently  part  more  readily  with 
their  heat. 

The  efficiency  of  stationary  flue-boilers  has  been  greatly  increased  by  the  introduc- 
tion of  the  so-called  Galloway  tubes  /  these  are  conical  tubes  placed  with  the  larger  end 
uppermost  across  the  flues,  sometimes  slightly  inclined.  Besides  furnishing  additional 
very  efficient  heating-surface  they  facilitate  greatly  the  circulation  of  the  water  and  act 
as  stiff  stays  ;  in  this  latter  capacity  they  are  particularly  useful  when  the  flues  have 
an  elliptical  cross-section.  The  introduction  of  these  tubes  into  old  flue-boilers  has 
often  produced  a  remarkable  improvement  in  their  steaming  capacity ;  but,  on  the 
other  hand,  they  make  the  flues  more  difficult  to  clean  and  repair,  so  that  the  accumu- 
lation of  soot  and  dirt  may  actually  cause  a  diminution  of  the  efficiency  of  the  heating- 
surface,  while,  at  the  same  time,  the  obstructions  to  the  draught  diminish  the  rate  of 
combustion.  Similar  tubes  are  sometimes  placed  in  the  back-connections  of  marine 

260 


SEC.  2.  FLUES  ASD  TUBES.  261 

boilers,  especially  when  there  is  one  back-connection  common  to  all  the  furnaces  of  a 
boiler. 

Flue-boilers  are  bulky  and  heavy,  and  the  large  amount  of  water  contained  in  them 
makes  it  impossible  to  get  up  steam  quickly.  To  remedy  these  defects,  which  are 
often  of  vital  importance  in  a  marine  boiler,  it  became  necessary  to  reduce  the  length  of 
the  flues,  and  to  increase  the  proportion  of  their  superficial  area  to  their  cross-area  by 
subdividing  each  flue  into  a  number  of  narrow  passages. 

In  the  Lamb  and  Sumner  boiler  the  flues  returned  over  the  furnaces  and  consisted 
of  a  number  of  narrow,  flat-sided  passages,  separated  by  equally  narrow  water-spaces, 
from  If  to  2  inches  wide  in  the  clear,  and  from  36  to  45  inches  high.  The  flat  sides 
were  held  by  stay-rivets  passing  through  the  smoke-passages.  These  boilers  were  in 
great  favor  some  years  ago ;  the  flat  sides  of  the  water-spaces  were  easily  scaled,  and 
the  flues  were  not  so  soon  obstructed  by  soot  as  small  tubes  ;  but  the  narrow  passages 
were  inaccessible  for  repairs  in  case  of  leaks,  and  corrosion  destroyed  them  rapidly. 
These  boilers  have  now  gone  out  of  use. 

At  the  present  day  it  is  the  nearly  universal  practice  to  get  the  principal  quantity  of 
heating-surface  in  marine  boilers  by  the  use  of  cylindrical  tubes  varying  from  2  to  4 
inches  in  diameter. 

2.  Relative  Advantages  of  Flues  and  Tubes  for  Marine  Boilers. — The  prin 
cipal  advantages  possessed  by  tubular  over  flue  boilers  may  be  shortly  summed  up  as 
follows  :  Less  weight  and  space  is  required  for  boilers  of  equal  economic  and  potential 
evaporative  efficiency  ;  steam  can  be  raised  rapidly  after  the  fires  are  started,  in  conse- 
quence of  the  relatively  small  weight  of  water  contained  in  the  tubular  boiler  in  pro- 
portion to  the  extent  of  heating-surface ;  the  small  tubes  have  far  greater  strength  than 
flues  ;  the  tubes  are  less  liable  to  leakage  from  the  absence  of  riveted  joints ;  they  can 
be  made  of  material  not  liable  to  corrosion,  and  are  easily  removed  and  replaced  ;  the 
escape  of  steam  or  water  from  a  ruptured  tube  seldom  produces  serious  effects,  and  the 
leak  can  often  be  temporarily  stopped  without  interrupting  the  working  of  the  boiler. 

On  the  other  hand,  crowding  the  numerous  tubes  into  a  narrow  space,  and  the  rapid 
formation  of  steam  on  their  surfaces,  often  cause  foaming  or  priming,  affecting  very  un- 
favorably the  economic  performance  of  the  engine ;  a  large  portion  of  the  heating- 
surfaces  is  inaccessible  for  cleaning,  so  that  the  accumulation  of  scale  and  other  foreign 
matter  soon  impairs  the  evaporative  efficiency  of  the  surfaces,  and  causes  the  destruc- 
tion of  the  boiler  by  corrosion  or  the  burning  of  the  metal. 

3.  Various  Types  of  Tubular  Boilers. — There  exists  great  variety  in  the  arrange- 
ment of  tubes  within  the  boiler :  the  hot  gases  pass  either  through  them  or  around 


202  STEAM  BOILERS.  CHAP.  XI. 

them ;  tubes  may  be  horizontal,  vertical,  or  inclined,  and  may  be  arranged  above,  be- 
hind, or  at  the  sides  of  the  furnaces ;  they  are  generally  straight,  but  bent  and  spiral 
tubes  are  employed  in  some  types  of  boilers.  Examples  of  different  arrangements  of 
tubes  in  marine  boilers  have  been  given  and  their  advantages  and  disadvantages  dis- 
cussed in  chapter  vii. 

The  considerations  governing  the  location  and  position  of  the  tubes  in  marine  boilers 
may  be  summed  up  as  follows :  When  the  room  in  the  length  and  breadth  of  the  vessel 
available  for  the  boilers  is  limited  the  tubes  must  be  arranged  directly  over  the  fur- 
naces ;  when,  on  the  contrary,  it  is  essential  to  keep  the  boilers  as  low  as  possible,  the 
tubes  have  to  be  arranged  behind  or  alongside  the  furnaces.  Every  change  in  the 
direction  of  the  current  of  the  hot  gases  passing  from  the  furnace  to  the  chimney  in- 
volves a  loss  of  head,  or,  in  other  words,  diminishes  the  draught,  and  consequently  the 
maximum  rate  of  combustion.  The  resistance  to  the  flow  of  gases  through  a  tube  is 
mainly  due  to  friction  against  its  inner  surface ;  the  resistance  to  the  flow  of  gases 
'between  a  nest  of  water- tubes  is  relatively  much  greater,  being  due  to  friction  against 
the  outer  surfaces  of  the  tubes,  to  the  loss  of  head  produced  by  the  successive  changes 
in  the  cross-area  of  the  passages,  and  to  the  counter-currents  caused  by  the  impinge- 
ment of  the  gases  on  the  tubes.  The  evaporative  efficiency  of  the  vertical  water-tube  is 
superior  to  that  of  the  fire-tube,  because  the  hot  gases  impinging  on  the  surface  of  the 
former  part  with  their  heat  much  more  readily  than  the  gases  which  move  in  a  direction 
parallel  to  the  axis  of  the  fire-tube.  The  evaporative  efficiency  of  vertical  fire-tubes 
is  inferior  to  that  of  horizontal  fire-tubes,  because  the  steam  escapes  more  readily  from 
the  most  efficient  portion — i.e.,  the  top — of  the  latter,  and  the  tendency  to  an  equali- 
zation of  the  temperature  of  the  mass  of  gases  by  convection  is  greater  in  the  horizontal 
than  in  the  vertical  fire-tube  ;  for  the  gases  which  are  cooled  down  by  contact  with  the 
upper  portions  of  the  surface  of  the  ho'rizontal  tube  sink  by  gravity  and  are  replaced 
by  hotter  gases,  while  in  the  vertical  tube  the  gases  occupying  the  central  part  of  the 
tube  are  likely  to  pass  through  the  tube  without  coming  in  contact  with  its  sides. 
Horizontal  water-tubes  are  inefficient  and  dangerous  with  a  rapid  evaporation,  on  ac- 
count of  the  difficulty  which  the  steam  experiences  in  escaping  from  them.  Externally- 
heated  horizontal  tubes  can,  however,  be  used  safely  for  the  purpose  of  drying  or  super- 
heating steam.  Scale  is  easily  removed  from  the  inner  surface  of  water-tubes,  but  fire- 
tubes  are  more  easily  swept  of  soot  and  ashes.  With  vertical  tubes  the  water-level  can 
be  safely  carried  below  the  upper  tube-sheet,  while  horizontal  tubes  are  quickly  de- 
stroyed when  the  upper  rows  are  bared,  of  water. 

4.  Dimensions  and  Spacing  of  Tubes. — The  width  of  the  space  available  for 


SEC.  4.  FLUES  AND  TUBES.  263 

each  nest  of  tubes  is  generally  limited  by  the  width  of  the  furnace  ;  and  its  height  and 
the  length  of  the  tubes  are  dependent  not  only  on  the  dimensions  of  the  shell  of  the 
boiler,  but  also  on  economical  considerations.  In  proportioning  the  dimensions  of  the 
tubes  and  their  spacing  the  following  conditions  must  be  kept  in  view  : 

First.  The  opening  through  or  between  the  tubes  must  be  sufficient  for  the  passage 
of  the  products  of  combustion  ;  the  calorimeter  determines  to  a  great  extent  the  rate  of 
combustion  in  the  furnace,  and  varies  in  marine  boilers  from  |  to  £  of  the  area  of  the 
grate-surface. 

Second.  The  tubes  must  present  a  sufficient  amount  of  heating-surface.  The  ratio 
of  the  heating-surface  to  the  rate  of  combustion  affects  the  economic  and  potential  eva- 
porative efficiency  of  the  boiler ;  and  the  evaporative  efficiency  of  the  tube-surface 
decreases  rapidly  from  the  end  where  the  gases  enter  to  where  they  are  discharged  into 
the  uptake.  In  the  ordinary  types  of  return-tubular  boilers,  in  which  the  total  heating- 
surface  is  equal  to  25  times  the  grate-surface,  the  proportion  of  the  tube-surface  to  the 
grate-surface  is  very  nearly  as  18  to  1.  The  heating-surface  of  a  tube  is  to  be  calculated 
for  the  side  in  contact  with  the  hot  gases ;  therefore  it  depends  on  the  outer  circum- 
ference of  a  water-tube,  and  on  the  inner  circumference  of  a  fire-tube. 

Third.  The  spaces  between  the  tubes  must  be  arranged  with  regard  to  facility  for 
scaling  and  cleaning,  and  to  the  free  escape  of  the  steam  as  soon  as  formed.  The  upper 
rows  of  horizontal  fire-tubes  and  the  upper  part  of  vertical  tubes  are  surrounded  or 
filled  by  the  mass  of  steam-bubbles  rising  from  the  lower  heating-surfaces,  and  are  on 
this  account  less  efficient  as  heating-surfaces.  Isherwood  found  by  experiment  that 
the  gases  emerging  from  the  upper  rows  of  tubes  were  often  nearly  300°  Fahr.  hotter 
than  those  leaving  the  lower  rows  of  tubes.  For  this  reason  it  is  advantageous  to  make 
the  nest  of  tubes  as  low  as  possible. 

The  outside  diameter  of  the  vertical  water- tubes  in  the  Martin  boiler  (see  Plate  VI.) 
is  generally  2  inches,  and  they  are  spaced  from  3  inches  to  3J  inches  apart  from  cen- 
tre to  centre  on  a  line  across  the  tube-box  ;  when  the  clear  space  between  two  adjoining 
tubes  is  made  less  than  one  inch  the  draught  of  the  boiler  becomes  seriously  impaired. 
On  a  line  in  the  direction  of  the  length  of  the  tube-box,  the  closeness  of  the  spacing  of 
the  tubes  is  limited  only  by  the  possibility  of  boring  the  holes  in  the  tube-plates  without 
impairing  the  stiffness  of  the  plates  too  much  ;  with  2-inch  tubes  the  distance  between 
the  centres  is  seldom  less  than  2||  inches.  The  length  of  the  tubes  depends  on  the 
amount  of  heating-surface  required,  but  is  limited  by  the  height  of  the  boiler;  the 
evaporative  efficiency  of  short  tubes  is  greater  than  that  of  longer  tubes  having  the 
same  diameter  and  presenting  an  equal  amount  of  heating-surface. 


264  STEAM  BOILERS.  CHAP.  XI. 

In  the  boiler  represented  on  Plate  VI.  the  tubes  are  2  inches  in  diameter  and  32 
inches  long  between  the  tube-sheets ;  they  are  spaced  3J  inches  apart  from  centre  to 
centre  across  the  tube-boxes,  and  2f£  inches  apart  from  centre  to  centre  in  the  rows 
running  lengthwise  the  tube-boxes.  Each  tube-box  is  of  the  same  width  as  the  fur- 
naces— viz.,  36  inches — and  is  85|  inches  long,  containing  in  this  space  306  brass  tubes 
with  an  aggregate  heating-surface  of  427.25  square  feet. 

These  tubes  have  sometimes  been  arranged  so  that  the  longitudinal  rows  formed 
zigzag  lines,  in  order  that  the  gases  might  impinge  on  a  greater  amount  of  surface ; 
but  what  is  gained  in  evaporative  efficiency  of  tube-surface  in  such  a  case  is  lost  in 
the  rate  of  combustion.  The  most  serious  objection  to  this  arrangement  is  the  impossi- 
bility of  sweeping  the  spaces  between  the  tubes  properly. 

The  diameter  of  fire-tubes  in  marine  boilers  varies  ordinarily  between  2f  inches 
and  4  inches.  Horizontal  tubes  of  smaller  diameter  than  2£  inches  would  soon  become 
choked  with  ashes  and  soot,  unless  forced  draiight  is  used,  as  in  locomotives,  when  the 
diameter  is  reduced  sometimes  to  1£  inches.  Vertical  fire-tubes  may  be  made  of  smaller 
diameter  than  horizontal  tubes,  since  they  are  not  obstructed  by  soot  and  ashes  like  the 
latter.  When  bituminous  coal  is  the  fuel  used  tubes.of  larger  diameter  become  necessary 
than  when  anthracite  is  burned,  on  account  of  the  great  quantity  of  soot  produced  by 
the  former  coal.  Large  tubes  offer  less  resistance  to  the  flow  of  the  gases,  and  admit  of 
a  higher  rate  of  combustion  with  natural  draught,  than  smaller  ones  ;  but  with  the  latter 
a  larger  amount  of  heating-surface  can  be  got  in  a  given  space.  When  the  diameter  of 
the  fire-tube  is  increased  it  becomes  necessary  to  increase  its  length  in  the  same  propor- 
tion, in  order  to  preserve  the  same  ratio  between  the  surface  and  the  cross-area  of  the 
tube,  or,  in  other  words,  between  the  heating-surface  and  the  quantity  of  gas  passing 
through  each  tube. 

Experiments  by  Dewrance,  Woods,  and  C.  W.  Williams  demonstrated  the  rapid 
decrease  in  the  evaporative  efficiency  of  each  additional  length  of  tubes.  After  a  cer- 
tain limit  is  reached  the  gain  in  the  evaporative  efficiency  of  a  tube  through  an  increase 
of  its  length,  and  consequently  of  its  surface,  is  trifling  compared  with  the  additional 
bulk,  weight,  and  cost  of  the  boiler,  while  the  additional  friction  retards  somewhat  the 
draught.  Since  for  equal  economic  evaporative  efficiency  the  amount  of  heating-sur- 
face must  be  proportioned  to  the  quantity  of  hot  gases  in  contact  with  it,  the  length  of 
the  tube  must  depend  on  the  diameter  of  the  tube  and  the  rate  of  combustion.  In  loco- 
motive boilers,  with  forced  draught,  the  length  of  tubes  is  made  often  120  times  their 
diameter.  Wilson  recommends  that  with  natural  draught  the  length  of  tubes  should 
not  be  greater  than  24  times  their  diameter.  This  is,  however,  less  than  the  usual  prac- 


SEC.  5.  FLUES  AND  TUBES.  265 

tice,  and  Isherwood  says :  "  For  a  tube  3  inches  diameter  a  length  of  38  diameters  will 
be  found  a  good  proportion  with  a  rate  of  combustion  exceeding  12  Ibs.  of  anthracite 
per  hour  in  the  hold  of  a  vessel." 

The  clear  space  between  adjoining  horizontal  fire-tubes  varies  between  one-half  and 
one-third  the  diameter  of  the  tubes.  To  facilitate  the  washing  and  the  scaling  between 
the  tubes,  as  well  as  the  escape  of  the  steam-bubbles  as  soon  as  generated,  horizontal 
tubes  in  marine  boilers  should  always  be  arranged  in  vertical  rows,  and  not  in  diagonal 
or  zigzag  rows,  which  is  sometimes  done  for  the  purpose  of  crowding  a  greater  number 
of  tubes  into  a  given  space.  In  locomotive  boilers,  where  fresh  water  is  used  and  the 
steam  generated  on  the  furnace-crown  has  not  to  pass  between  the  rows  of  tubes,  the 
latter  are  frequently  arranged  in  zigzag  lines. 

In  Skime?  s  differential  tubular  boiler  the  horizontal  fire- tubes  in  each  successive  hori- 
zontal row,  from  the  bottom  upwards,  decreased  in  diameter  \  inch.  The  boilers  of  U.  S. 
S.  Tippecanoe  and  class  had  eight  horizontal  rows  of  tubes  over  each  furnace  ;  the  out- 
side diameter  of  the  tubes  was  3£  inches  in  the  bottom  row  and  2f  inches  in  the  top  row ; 
the  spacing  of  the  tubes  in  a  horizontal  direction  was  uniform — viz.,  4f  inches  from 
centre  to  centre.  This  arrangement  facilitates  greatly  the  escape  of  steam,  and  to  some 
extent  the  scaling  of  the  tubes,  and  was  also  intended  to  equalize  the  evaporative  effi- 
ciency of  the  heating-surface  in  each  horizontal  row  of  tubes  ;  but  its  practical  disad- 
vantages are  great — viz.,  to  form  the  holes  eight  sizes  of  drills  or  eight  adjustments  of 
the  boring-cutters  are  required  ;  eight  sizes  of  tubes  are  used,  and  three  or  four  sizes  of 
expanding-tools ;  spare  tubes  and  expanding-tools  of  assorted  sizes  have  to  be  carried, 
and  tube-brushes  of  assorted  sizes  are  used.  With  these  drawbacks  it  is  not  strange 
that  the  system  has  not  come  into  favor. 

When  a  large  amount  of  heating-surface  is  required  it  is  often  difficult  to  propor- 
tion the  number  and  dimensions  of  the  tubes  in  such  a  manner  in  the  given  space  as  to 
get  at  the  same  time  the  best  ratio  of  calorimeter  to  grate-surface.  In  such  a  case  the 
calorimeter  of  fire-tubes  may  be  reduced  by  driving  ferrules  into  the  ends  of  the  tubes, 
at  the  back  end  of  return-tube  boilers,  and  at  the  front  end  of  locomotive  boilers.  In 
the  latter  boilers,  when  iron  tubes  are  used,  their  diameter  is  sometimes  reduced  at  the 
front  end  by  swaging,  as  illustrated  on  Plate  XXIV.  When  the  opening  through  the 
tubes  is  contracted  by  these  means  the  sweeping  of  the  tubes  is  made  more  difficult ; 
the  effect  of  the  ferrules  in  increasing  the  holding  power  of  the  tubes  in  the  tube-plates 
will  be  discussed  further  on. 

5.  Iron,  Steel,  Brass,  and  Copper  Tubes. — The  tubes  of  marine  boilers  are 
generally  made  of  brass  or  iron  ;  steel  tubes  have  also  been  introduced  of  late.  Copper 


266  STEAM  BOILERS.  CHAP.  XI. 

tubes  were  formerly  used  for  locomotive  boilers,  but  they  wore  out  rapidly  in  conse- 
quence of  the  mechanical  action  of  the  cinders  carried  through  them  at  a  great  velocity 
by  the  strong  draught ;  the  great  difference  in  the  expansion  of  iron  and  copper  by 
heat  produces  also  inconveniences  in  the  combination  of  the  two  metals  in  steam 
boilers.  The  use  of  copper  tubes  in  marine  boilers  is  prevented  by  the  lively  galvanic 
action  which  takes  place  when  copper  is  in  contact  with  iron  in  the  presence  of  salt 
water ;  they  are  used,  however,  sometimes  in  the  steam-space  as  superheating-tubes,  for 
which  purpose  the  great  thermal  conductivity  of  copper  and  its  freedom  from  corrosion 
give  them  great  advantages. 

Lap-welded  wrought-iron  tubes  are  still  extensively  used  in  boilers  of  merchant  ves- 
sels, but  seamless  drawn-brass  tubes  are  now  almost  exclusively  used  in  the  boilers  of 
naval  vessels.  Brass  tubes  possess  many  of  the  advantages  of  copper  tubes,  without 
their  disadvantages :  they  are  very  ductile,  their  thermal  conductivity  is  greater  than 
that  of  iron,  and  they  expand  less  under  the  influence  of  heat  than  copper  ;  they  suffer 
little  from  wear,  are  not  subject  to  corrosion,  and  do  not  appear  to  produce  serious  gal- 
vanic action  in  marine  boilers.  Iron  tubes  have  the  advantage  of  lower  first  cost  over 
brass  tubes.  Since  iron  tubes  are  not  so  easily  injured  by  biirning  as  brass  tubes  when 
the  water-level  falls  below  the  tubes,  a  few  of  them  are  often  used  as  stay-tubes  in  hori- 
zontal-tubular boilers  to  hold  the  tube-sheets,  while  the  principal  portion  of  the  tubes 
is  of  brass.  For  vertical  water-tubes  brass  should  always  be  used,  because  iron  tubes 
are  rapidly  corroded  by  the  sulphuric  acid  which  is  distilled  from  the  soot  by  moisture, 
runs  down  the  tubes,  and  collects  at  their  lower  end. 

With  vertical  brass  tubes  the  water-level  can  be  carried  safely  below  the  upper  tube- 
plate,  as  was  proved  by  several  interesting  experiments  conducted  by  Chief  Engineer 
Isherwood,  U.S.N.,  and  recorded  in  '  Experimental  Researches,'  vol.  ii.  In  the  trial  of 
the  vertical  water-tube  boiler  of  the  U.  S.  S.  Wyoming  the  water-level  was  carried,  at 
different  times,  7f,  15,  and  22 £  inches  below  the  top  tube-plate.  "  The  whole  length  of 
the  tubes,  which  were  of  seamless  brass,  was  30  inches.  The  only  damage  done  was 
when  the  water  was  carried  22f  inches  below  the  top  tube-plate,  and  then,  after  a  trial 
of  72  consecutive  hours,  burning  at  the  rate  of  15.77  Ibs.  of  anthracite  per  square  foot 
of  grate  per  hour,  the  joints  of  only  the  two  rows  of  tubes  next  the  back  smoke-con- 
nection were  loosened.  Neither  the  brass  of  the  tubes  nor  the  iron  of  the  tube-plate 
and  of  the  exposed  portions  of  the  back  smoke-connections  was  in  the  least  degree 
injured." 

Iron  tubes  are  more  apt  to  be  injured  than  brass  tubes  in  the  process  of  securing 
them  in  the  tube-sheets  by  expanding  their  ends,  and  leakage  with  its  attendant  evils  ia 


SEC.  5.  FLUES  AND  TUBES.  267 

more  frequent  with  them.  Iron  tnbes,  being  relatively  thin,  are  destroyed  by  corrosion 
much  sooner  than  the  plates  of  boilers.  The  thickness  of  boiler-tnbes  varies  from  No. 
8  to  14  of  the  Birmingham  gauge,  according  to  their  diameter,  the  material  of  which 
they  are  made,  the  steam-pressure  and  the  kind  of  pressure,  bursting  or  collapsing,  to 
which  they  are  exposed. 

Coppered  and  tinned  iron  tubes  have  been  tried,  but  they  have  not  been  long  enough 
in  use  to  warrant  an  opinion  regarding  their  durability. 

Tubes  made  of  soft  steel  are  either  lap-welded  or  drawn  seamless.  They  are  more 
expensive  than  iron  tubes,  and  whether  they  can  be  made  lighter  than  the  latter  de- 
pends principally  on  their  liability  to  corrosion,  regarding  which  fact  opinions  are  much 
divided. 

When  the  tubes  are  new  and  clean  their  thickness  and  the  thermal  conductivity  of 
the  metal  of  which  they  are  composed  exert,  no  doubt,  an  influence  on  their  evapora- 
tive efficiency  ;  but  as  soon  as  their  surfaces  become  covered  with  deposits  of  soot  and 
scale  they  become  of  equal  value  in  this  respect. 

Drawn  seamless  tubes  are  made  from  short  cylinders  through  which  a  small  hole  has 
been  bored  or  left  in  casting.  The  cylinder,  being  passed  through  several  sets  of  dies 
very  slightly  decreasing  in  size,  and  over  mandrels  very  gradually  increasing  in  diame- 
ter, is,  by  a  succession  of  steps  and,  in  the  case  of  steel  tubes,  after  frequently  under- 
going the  annealing  process,  drawn  out  into  a  long,  thin  tube  of  the  desired  dimen- 
sions. The  process  is  not  severe  as  long  as  the  dies  are  in  good  order,  but  when  they 
are  in  the  least  degree  rough  great  heat  is  evolved  in  the  passage  of  the  metal.  An  ob- 
jection to  the  method  in  the  case  of  brass  is  that  the  smallest  defect  is  drawn  out  into  a 
scratch  which  becomes  a  source  of  weakness.  Latent  defects,  however,  can  be  dis- 
covered in  the  testing  which  all  tubes  should  undergo  at  the  works ;  this  test  should 
have  reference  to  the  use  to  which  the  tubes  are  to  be  put — those  intended  for  water- 
tubes  should  withstand  an  internal  bursting  pressure,  while  those  intended  for  fire-tubes 
must  be  able  to  resist  collapse. 

Copper  and  brass  tubes  were  at  first  made  of  long,  narrow  sheets  bent  into  the  cylin- 
drical form  and  brazed  at  the  joint.  Wrought-iron  ones  are  now  constructed  of  narrow 
sheets  brought  to  a  welding-heat  and  passed  through  rollers.  Drawn  tubes  are  gene- 
rally slightly  conical  to  permit  their  being  easily  delivered  from  the  mandrel ;  and  this 
feature  has  been  exaggerated  by  some  inventors,  who  make  the  outside  diameters  of 
tubes  which  are  intended  to  be  removable  for  the  purpose  of  scaling  i  inch  larger  at  the 
front  than  at  the  back  end. 


268 


STEAM  BOILERS. 


CHAP.  XI. 


TABLE  XXXIII. 

SIZES  AND  WEIGHTS  OF  LAP- WELDED  IRON  BOILER-TUBES  OF  STANDARD  GAUGE  MANUFACTURED 

BY  THE  NATIONAL  TUBE  WORKS  COMPANY. 


Outside  diameter. 
Inches. 

Thickness. 

Weight  per  foot. 
Pounds. 

Birmingham  wire-gauge. 

Inches. 

4 

14 

•0875 

1-25 

if 

13 

.1000 

1.  60 

2 

13 

.1000 

2.OO 

«i 

13 

.1000 

2.IO 

4 

12 

.1125 

2-75 

4 

12 

.1125 

3.00 

3 

12 

.1125 

3-33 

3± 

II 

.1256 

4.00 

3* 

II 

.1250 

4-33 

3f 

II 

.1250 

4-63 

4 

IO 

.1406 

5-5° 

4 

IO 

.1406 

6.00 

5 

9 

•1563 

7-25 

6 

8 

.1719 

9-33 

7 

8 

.1719 

12.50 

8 

8 

.1719 

15.00 

9 

7 

•  1875 

i7-3i 

10 

6 

.2031 

20.80 

These  tubes  are  made  of  the  best  American  charcoal  hammered  iron  and  are  stamped 
The  greatest  regular  length  of  these  tubes  is  18  feet ;  lap-welded  tubes  of  any 
thickness  and  size  up  to  18  inches  diameter,  and  of  a  length  exceeding  18  feet,  manu- 
factured to  order. 

Lap-welded  steel  boiler-tubes  are  made  from  1£  to  18  inches  in  diameter. 


SEC.  5. 


FLUES  AND  TUBES. 


269 


TABLE  XXXIV. 

LAP-WELDED  AMERICAN  CHARCOAL-IRON  BOILER-TUBES  MANUFACTURED 
BY  MORRIS,  TASKER  &  Co.,  1877. 

Table  of  Standard  Dimensions. 


External 

diameter. 

Inches. 

Standard 
thickness. 

Inches. 

Nearest 
B.  W.  G. 

Internal 
circumference. 

Inches. 

External 
circumference. 

Inches. 

Internal  area  of 
cross-  section. 

Square  inches. 

External  area  of           Weight 
cross-section.            per  foot. 

Square  inches,  j        Pounds. 

I 

.072 

15 

2  689 

3-142 

0-575 

0.785 

0.708 

if 

.072 

15 

3-474 

3-927 

0.960 

1.227 

0.900 

4 

.083 

14 

4.191 

4.712 

1.396 

1.767 

1.250 

if 

•°95 

13 

4.901 

5-498 

1.911 

2.405 

1.665 

2 

.098 

13 

5.667 

6.283 

2-556 

3-142 

1.981 

»i 

.098 

13 

6.484 

7.069 

3-3  '4 

3-976 

2.238 

4 

.IO9 

12 

7.172 

7-854 

4.094 

4.909 

2-755 

4 

.109 

12 

7-957 

8.639 

5-°39 

5-940 

3-045 

3 

.109 

12 

8-743 

9-425 

6.083 

7.069 

3-333 

3i 

.II9 

II 

9.462 

IO.2IO 

7-125 

8.296 

3-958 

-       3i 

.119 

II 

10.248 

10-995 

8-357 

9.621 

4-272 

3* 

.119 

II 

".033 

IIjSl 

9.687 

11.045 

4-59° 

4 

•130 

10 

"-753 

12.566 

10.992 

12.566 

5-320 

4 

.130 

10 

i3-323 

14-137 

14.126 

I5-904 

6.010 

5 

.I4O 

9i 

14.818 

15-708 

17-497 

I9-635 

7.226 

6 

•IS1 

9 

17.904 

18.849 

25-509 

28.274 

9-346 

7 

.172 

8* 

20.914 

21.991 

34-8o5 

38.484 

12.435 

8 

.182 

8 

23-989 

25-T32 

45-795 

50.265 

15.109 

9 

•193 

7f 

27-055 

28.274 

58.291 

63.617 

18.002 

10 

.214 

4 

30.074 

31.416 

71-975 

78.540 

22.190 

ii 

.220 

5 

33-  '75 

34-557 

87-479 

95-033 

25.489 

12 

.229 

4* 

36.260 

37-699 

103.749 

113.097 

28.516 

!3 

.238 

4 

39-345 

40.840 

123.187 

132.732 

32.208 

14 

.248 

3i 

42.414 

43-982 

143.189 

I53.938 

36.271 

15 

•259 

3 

4S-496 

47.124 

164.718 

176.715 

40.612 

16 

.271 

*i 

48.562 

50.265 

187.667 

201.062 

45-!99 

i? 

.284 

2 

51.662           53-407 

212.227 

226.980 

49.902 

18 

.292 

4 

54.714           56.548         238.224 

254.469 

54.816 

J9 

.300 

i 

57-8o5           59-69°         265.903 

283.529 

59-479 

20 

.320 

i 

60.821           62.832         294.373 

3i4-I59 

66.765 

21 

•340 

O 

63-837           65.973         324.311 

346.361 

73-404 

The  thickness  of  tubes  can  be  varied  to  order.    Tubes  cut  to  specific  lengths  to  suit  purchasers  ;  lengths  greater 
than  eighteen  feet  at  special  rates. 


270 


STEAM  BOILERS. 


CHAP.  XT. 


TABLE  XXXV. 

REGULAR  SIZES  AND  WEIGHTS  OF  SEAMLESS  DRAWN  BRASS  AND  COPPER  TUBES  MANUFACTURED 

BY  AMERICAN  TUBE-WORKS,  BOSTON,  MASS.,  1879. 


Outside 
diameter. 

Length. 

Thickness 

Weight  per  foot. 

Outside 
diameter. 

Length. 

Thickness 

Weight  per  foot. 

Inches. 

Feet. 

Stub's  W.  G 

Pounds. 

Inches. 

Feet. 

Stub's  W.G 

Pounds. 

1 

Brass. 

Copper. 

Brass. 

Copper. 

f 

12 

18 

0.32 

0-34 

2  t 

* 

j  14 

i-97 

2.07 

12 

17 

0.47 

0.49 

8 

(  I2 

2-55 

2.68 

T5 

IO 

17 

0.50 

o-53 

j_ 

T  A 

\  14 

2.08 

2.19 

tt 

10 

IO 
IO 

17 

16 
16 

°-55 
0.64 
0.70 

0.58 
0.66 
0.74 

•1 

»4 

13 

(   12 

I'4 
/    12 

2.71 

2.20 
2.86 

2.85 
2-32 
3-oi 

1  i 

IO 

16 

0.79 

0.83 

2  i 

1  1 

.     13 

2.65 

2-79 

1  1. 

15 

j  14 

1.  12 

1.18 

1  o 

II 

3-31 

3-48 

(   12 

f 

1.44 

i-52 

2  i 

I  2 

13 

2.78 

2-93 

if 

12 

13 
12 

14 

I  12 

14 

1  12 

14 

i-25 
1.60 

1.36 
1.76 
1.48 

1.68 

i-43 
1.85 

1-56 

3 

12 
12 

II 

I'3 
i   II 

I13 
j    II 

3-49 
2-93 
3.66 
3.20 
4.01 

3-08 
3-85 
3-37 
4.22 

(  12 

1.92 

2  02 

i 

IO 

13 

3-34 

3-51 

if 

13 
13 
12 

14 

(   12 

14 

(  I2 

1.61 
2.07 
1.66 

2-15 
1.72 

1.69 
2.18 

i-75 
2.26 
1.81 

3i 
3* 

10 
IO 

I'" 
1   II 

I'3 
j   II 

4.18 
3-48 
4-35 
3-75 
4.70 

4.40 
3.66 
4-58 
3-95 
4-95 

iff 

12 

.     14 

2.23 
1.78 

2-35 
1.87 

4 

10 

\\\ 

4-3° 
5-4° 

4-53 
5.68 

2 

15 

12 

2.31 
1.84 

2-43 
i-94 

5 

10 

(12 
\    10 

6.18 
7-56 

6.50 
7.96 

12 

2-39 

2.51 

6 

IO 

I- 

7-44 

7-83 

\   10 

9.11 

9-59 

SEC.  6. 


FLUES  AND  TUBES. 


271 


These  tubes  are  polished,  both  inside  and  outside.  They  are  perfectly  cylindrical 
on  the  outside ;  the  bore  is  a  gradual  taper,  the  difference  in  diameter  being  two  wire- 
gauges  in  eleven  feet. 


TABLE  XXXVI. 
STUB'S  WIRE-GAUGE. 


Stub's  wire-gauge. 

I 

2 

3 

4 

5 

6 

7 

8 

9 

10 

ii 

12 

13 

14 

15 

16 

17 

18 

19 

20 

Fractions  of  an  inch,  . 

«/ 

*/ 

*/ 

H/ 

A/ 

« 

A* 

tt* 

A/ 

A* 

t* 

ft 

A/ 

A/ 

A* 

A/ 

A* 

A/ 

A* 

A/ 

NOTE. — f  means  full ;  b  means  bare. 

6.  Methods  of  expanding  Tubes.— The  tubes  are  generally  secured  in  the  tube- 
sheets  by  expanding  their  ends  by  means  of  a  special  tool,  which  forces  the  metal  of 
the  tubes  into  close  contact  with  the  circumference  of  the  holes  in  the  tube-plates,  and 
in  some  cases  forms  a  shoulder  on  the  tubes  inside  and  outside  the  tube-plates.  Some- 
times a  ferrule  is  driven  tightly  into  the  tube,  and  the  projecting  end  of  this  ferrule 
may  be  riveted  over  the  end  of  the  tube.  These  ferrules  add  much  to  the  tightness  and 
holding  power  of  the  tubes  in  the  plates,  but  contract  the  opening  for  draught  and  in- 
terfere with  the  sweeping  of  fire-tubes.  The  ends  of  the  tubes  are  annealed  before 
undergoing  the  process  of  expansion.  It  is  of  great  importance  that  the  joints  be- 
tween the  tubes  and  the  tube-plates  shall  be  made  perfectly  tight,  not  only  to  pre- 
vent leakage  with  its  attendant  evils,  but  also  to  make  the  tubes  act  as  efficient  stays 
for  the  tube-plates.  On  the  other  hand,  when  the  tube-plates  are  kept  too  rigidly  in 
position,  and  cannot  yield  in  obedience  to  the  expansion  of  the  tubes  in  the  direction  of 
their  length  with  an  increase  of  temperature,  the  tubes  must  have  a  chance  to  bend 
sidewise,  which  action  will  take  place  when  the  length  of  the  tubes  is  so  great  in  pro- 
portion to  their  diameter  that  they  sag  down.  The  thickness  of  the  tube-plates  must  be 
sufficient  to  afford  a  good  bearing  to  the  tubes  for  making  the  joint,  and  to  ensure 
proper  stiffness  in  the  plates  after  the  numerous  large  holes  are  drilled.  They  are  gene- 
rally made  at  least  \  inch  thick. 

The  centres  of  the  holes  being  marked  on  the  tube-sheets,  a  small  hole,  may  be 
punched  to  serve  as  a  guide  for  the  drill,  and  the  tube-holes  are  then  drilled  accurately 
circular  and  cylindrical  to  such  a  size  that  the  tubes  can  be  just  passed  through  by 
hand ;  if  the  holes  be  too  large  the  ends  of  the  tubes  might  have  to  be  expanded  so 
much  that  they  might  crack  or  be  strained,  causing  them  to  split  afterward.  The  hole, 


272 


STEAM  BOILERS. 


CHAP.  XL 


Fig.  128. 


after  being  drilled,  is  often  slightly  counterbored  at  the  outer  face  of  the  sheet ;  the 
edge  of  the  hole  is  then  smoothed  with  a  file  to  remove  burrs  and  inequalities,  which 
would  prevent  contact  all  around  and  dent  or  cut  the  tube-end.  The  tube,  which  is  a 
quarter  of  an  inch  longer  than  the  distance  between  the  outer  faces  of  the  two  sheets,  is 
then  put  in  place  so  that  each  end  protrudes  one-half  of  that  amount ;  the  expanding- 
tool  being  then  inserted  at  the  end,  the  tube  is  expanded,  sometimes  inside  and  outside 
the  tube-plate,  and  sometimes  riveted  over  slightly  on  the  outside  into  the  counterbore. 
Sometimes  the  tube-holes  are  bored  slightly  conical  for  the  purpose  of  increasing  the 
holding  power  of  the  tubes  (see  Plates  XXIII.,  XXIV.) 

Figure  128  represents  Raymond's  patent  recessed  tube-sheet.     The  tube-sheet  is 

made  very  thick  to  give  it  great  stiffness,  and  the 
tube-holes  are  countersunk,  so  that  the  tube-ends 
may  be  turned  over  within  the  recess.  In  this  man- 
ner the  tube-ends  in  the  combustion-chamber  are  less 
exposed  to  the  impingement  of  the  products  of  com- 
bustion, which  causes  them  to  wear  rapidly,  thus  de- 
stroying their  tightness  and  holding  power.  For  fur- 
ther protection  the  recess  may  be  filled  with  cement. 

Prosser's  expanding  -  tool  is  shown  on  Plate 
XXIII.,  and  acts  by  percussion.  It  consists  of  a 
circular  die  formed  by  several  truncated  sectors,  held 
together  loosely  by  a  ring,  which,  however,  is  large 
enough  to  permit  them  to  be  driven  asunder  by  a 
slightly  conical  mandrel  forced  between  them ;  the 
dies  are  provided. with  two  rounded  shoulders,  one  of 
which,  when  the  mandrel  is  driven,  enlarges  the  por- 


tion of  the  tube  within,  and  the  other  that  without,  the  plate.  The  mandrel  being 
backed  out  by  tapping  it  on  the  side  or  through  the  other  end  of  the  tube,  the  sectors 
are  released  and  turned  somewhat  and  the  mandrel  driven  in  again,  so  as  to  subject  all 
portions  of  the  tube-end  to  their  action. 

Dudgeorf  s  tube-expander  (see  Plate  XXIII.)  was  invented  1867,  and  is  very  exten- 
sively used.  It  consists  of  a  hollow  cylinder  of  less  diameter  than  the  tube,  and  pro- 
vided with  openings  to  receive  three  or  more  steel  rollers,  which  rest  inside  upon  a  cen- 
tral conical  mandrel.  A  guide-sleeve,  which  bears  against  the  tube-sheet,  is  secured  to 
the  hollow  cylinder  by  a  set-screw.  By  shifting  the  position  of  this  sleeve  the  ex- 
pander is  made  to  answer  for  any  thickness  of  tube-sheet.  By  inserting  the  tool  into 


SEC.  6. 


FLUES  AND  TUBES. 


273 


Fig.  129. 


the  tube  and  pressing  upon  and  revolving  the  mandrel  the  rollers  are  set  in  motion,  and, 
travelling  around  the  circumference  of  the  tube,  press  out  the  metal  of  the  tube-end 
gradually.  After  the  metal  of  the  tube  has  completely  filled  the  hole  it  is  compressed 
in  the  wake  of  the  tube-sheet,  but  it  yields  on  each  side  of  it,  forming 
shoulders  there  ;  this  action  is  shown  exaggerated  in  figure  129. 

These  expanders  are  made  of  different  sizes  to  fit  any  size  of  tube  be- 
tween the  limits  of  one  inch  and  seven  inches  external  diameter 
of  tube.  Fig.  130. 

Sometimes  the  rollers  are  shaped  as  in  figure  130 ;   this 
form,  it  is  claimed,  strains  the  metal  of  the  tube  less  than  the 
straight  rollers. 

In  still  another  tool  the  rollers  are  made  conical,  with  the  same  angle  as  the  man- 
drel, but  placed  in  an  opposite  direction,  so  as  to  set  the  tube  out  exactly  parallel  to 
its  axis. 

TweddeWs  hydraulic  tube-expander,  represented  in  figure  6,  Plate  XXII.,  is  said 
to  be  very  efficient  and  rapid  in  its  action.  The  water  is  pumped  in  at  A  directly 
from  a  small  hand-pump,  and  forces  outward  the  ram  B,  which  draws  the  hexagonal 
wedge  C  through  the  dies  D,  thus  expanding  the  tube  in  the  hole  in  the  tube-plate 
E.  Upwards  of  sixty  tube-ends  an  hour,  it  is  said,  can  be  finished  by  this  tool,  using 
a  pressure  of  from  1£  to  If  tons  on  the  square  inch. 

After  the  tube  has  been  expanded  the  ends  are  often  riveted  over  by  the  boot-tool, 
sketched  in  figure  131,  or,  in  large  and  accessible  tubes,  they  may  be  hammered  out 
with  a  round-headed  coppersmith's  hammer,  drawn 
in  figure  132.  It  is  objected  to  these  operations  that 
the  end  of  the  tube  becomes  thereby  a  brittle  ring, 
which  is  burned  off  by  the  action  of  the  fire,  espe- 
cially in  the  back-connection ;  such  a  result,  how- 
ever, indicates  rather  that  the  tube-ends  were  not 
sufficiently  annealed,  or  that  the  operation  had  been 
overdone  or  unskilfully  done.  The  operation  of  beading  should  not  be  commenced  till 
all  the  tubes  are  fixed  in  place  and  expanded,  since  the  stiffness  of  the  tube-plate  is 
greatly  increased  in  this  manner,  and  the  blows  of  the  hammer  jar  the  plate  less. 

The  beading  of  tube-ends  is  done  rapidly  and  smoothly  by  Selkirk's  tube-beader, 
illustrated  in  figure  7,  Plate  XXII.  It  is  worked  by  means  of  a  ratchet,  which  enables 
the  operator  to  work  in  very  confined  spaces.  The  beading  is  done  by  rolling  over  the 
tube-ends  against  the  tube-plate  gradually  with  an  increasing  pressure ;  this  method 


Fig.  131. 


Fig.  132. 


274  STEAM  BOILERS.  CHAP.  XI. 

obviates  the  danger  of  splitting  the  tube-ends,  jarring  severely  the  expanded  tubes,  and 
indenting  the  tube-plate  by  blows  with  the  hammer,  so  common  under  the  system  of 
hand-beading  in  ordinary  use.  The  action  of  the  tool  is  described  in  Engineering, 
June,  1877,  as  follows:  "The  fixing-piece  a  is  first  secured  firmly  in  the  boiler- tube  b 
by  the  action  of  the  nut  <?,  which  draws  the  coned  mandrel  d  outwards,  thrusting  the 
serrated  wedge-pieces  e  (three  in  number)  outward  against  the  tube  b.  The  body-piece 
f  is  then  brought  into  position,  so  that  the  beading- rollers  (three  in  number)  bear  upon 
the  edge  of  the  tube  at  b'.  A  considerable  pressure  is  then  brcmght  to  bear  upon  the 
beading-rollers  by  the  action  of  the  nut  7i,  friction-rollers,  i,  being  placed  between  the 
nut  h  and  the  body-piece  f  in  order  to  avoid  all  unnecessary  labor.  The  body-piece  f 
is  then  made  to  revolve  upon  the  fixing-piece  a  by  means  of  a  ratchet-wheel,  Jc,  and 
pawl,  I ;  the  body-piece  carries  with  it  the  beading- rollers  g,  and  a  very  perfect  bead  is 
thus  formed  quickly  upon  the  end  of  the  tube  as  shown  at  &'." 

In  using  the  expanding-tools  great  care  must  be  exercised  not  to  carry  the  operation 
farther  than  necessary  to  secure  tightness.  The  process  of  expanding  by  means  of  the 
Prosser  tool,  when  carried  too  far,  strains  the  metal  severely  and  may  cause  the  tube- 
ends  to  split.  The  Dudgeon  tool  becomes  a  dangerous  instrument  in  the  hands  of  an 
inexperienced  or  careless  person,  since  the  operation  of  rolling  out  the  metal  may  be 
continued  till  the  tube-ends  are  entirely  cut  off  without  giving  warning.  To  prevent 
this  the  taper  mandrel  often  carries  a  loose  collar,  which  may  be  secured  in  any  posi- 
tion by  means  of  a  set-screw,  and  thus  limit  the  distance  which  the  mandrel  may  enter 
the  tool  and  force  out  the  rollers. 

In  securing  boiler-tubes  it  should  be  taken  into  consideration  in  which  direction  the 
pressure  tends  to  force  the  tube-sheets  ;  thus,  in  the  vertical  water-tube  boiler,  the  ten- 
dency being  to  force  the  tube-sheets  together,  it  would  seem  that  the  Prosser  expand- 
ing-tool,  which  forms  a  shoulder  within  the  sheet,  would  be  the  preferable  one  to  be 
used  ;  but  in  the  fire-tube  boiler  the  steam  exercises  pressure  tending  to  force  the  tube- 
sheets  off  the  ends  of  the  tubes,  and  here  it  is  evident  that  riveting  over  the  ends  of  the 
tubes  increases  greatly  their  holding  power,  while  the  offset  within  the  sheet  adds  to 
their  tightness.  The  holding  power  of  expanded  tubes  is,  however,  ample  without 
riveting  their  ends  oVer,  as  shown  by  experiment. 

7.  Stay-tubes. — Formerly  it  was  often  thought  necessary  to  secure  the  tube-plates 
by  stay-rods,  designed  to  take  the  whole  strain  due  to  the  pressure  on  the  plates  ;  but, 
by  reference  to  the  experiments  recorded  in  section  9  of  this  chapter,  it  will  be  seen 
that  the  simple  process  of  expanding  the  ends  of  tubes  gives  them  sufficient  holding 
power  to  enable  them  to  act  as  efficient  stays  for  the  tube-sheets. 


SBC.  7.  FLUES  AND  TUBES.  275 

In  the  boilers  of  U.  S.  S.  Nipsic,  represented  on  Plate  XII.,  special  stay-tubes 
are  provided  to  support  the  tube-plates  at  the  points  where  an  additional  strain  is 
thrown  on  them  by  the  pressure  acting  on  the  centre  manhole-plate  at  the  front  tube- 
plate,  and  on  the  stay-dome  at  the  back  tube-plate.  These  stay -tubes  are  of  brass  like 
the  other  tubes,  and  have  the  same  diameter  and  thickness,  but  their  holding  power  is 
increased  by  beading  over  their  ends  after  being  expanded  with  the  Dudgeon  tool ;  for 
this  purpose  the  tubes  are  made  about  one-quarter  inch  longer  than  the  other  tubes. 
Such  stay-tubes  are  sometimes  made  of  iron,  so  as  to  be  less  easily  injured  by  burning 
in  case  the  water  should  get  low  in  the  boiler ;  but  to  place  these  iron  tubes  among  a 
mass  of  closely-spaced  brass  tubes  seems  hazardous,  on  account  of  their  increased  lia- 
bility to  corrosion. 

The  practice  of  providing  special  stay-tubes  secured  by  screw-threads  and  nuts  pre- 
vails still  to  a  great  extent  in  boilers  where  the  steam-pressure  exceeds  45  Ibs.  per 
square  inch.  In  English  boilers  these  stay-tubes  are  generally  placed  not  more  than  18 
inches  apart  from  centre  to  centre.  At  the  front  end  these  tubes  are  often  secured  by 
two  nuts,  one  inside  and  one  outside  the  tube-plate  ;  the  other  end,  exposed  to  the  in- 
tense heat  prevailing  in  the  back-connection,  is  secured  by  a  single  nut  and  by  screwing 
the  tube  into  the  tube-plate  with  about  eleven  threads  to  the  inch.  These  stay-tubes 
are  generally  of  the  same  external  diameter  as  the  other  tubes,  but  thicker. 

The  boilers  of  the  steamer  Atrato,  built  by  James  Watt  &  Co.  in  1872,  and  designed 
to  be  worked  with  a  steam-pressure  of  60  Ibs.  per  square  inch,  had  tube-plates  f  inch 
thick,  brass  tubes  4  inches  in  diameter  outside,  spaced  5f  inches  from  centre  to  centre. 
Each  tube-sheet  contained  four  stay-tubes,  spaced  16J  inches  apart  according  to  the 
following  directions : 

"The  stay-tubes  are  to  be  screwed  into  the  back  tube-plate  with  a  nut  on  the  out- 
side, and  there  are  to  be  two  nuts  on  the  front  end,  one  inside  and  one  outside.  All 
tubes,  including  stay-tubes,  to  be  ferruled  at  the  back  end.  Tubes  are  to  be  one-eighth 
inch  larger  in  diameter  at  front  end,  to  render  it  easier  to  draw  them  when  they  have  a 
scale  on.  Back  tube-plates  to  have  tapered  holes  into  which  the  tubes  will  be  ex- 
panded. Back  end  of  tubes  to  be  beaded ;  front  end  need  not  be.  Both  ends  may  be 
put  in  with  Dudgeon's  tool,  if  advisable.  Stay-tubes  to  be  i  incl^  thick  ;  others  No.  8 
B.  W.  G.  Total  number  of  stay-tubes,  48 ;  of  others,  432." 

In  the  boilers  of  the  steamer  Lord  of  the  Isles,  represented  on  Plate  XV.,  the  out- 
side diameter  of  the  stay-tubes  is  4  inches,  while  that  of  the  other  tubes  is  3£  inches. 
The  stay-tubes  are  made  £  inch  thick,  with  a  thread  cut  into  the  body  of  the  tube, 
leaving  an  effective  outside  diameter  of  3f£  inches,  and  an  inside  diameter  of  3J  inches. 


276  STEAM  BOILERS.  CHAP.  XL 

8.  Devices  for  rendering  Boiler-tubes  Removable. — Many  devices  have  been 
tried  to  secure  boiler-tubes  in  the  tube-plates  in  such  a  manner  as  to  make  it  possible  to 
remove  them  without  injuring  them  and  to  replace  them  easily,  in  order  to  clean  their 
surfaces  thoroughly  or  to  make  the  crown-sheets  of  the  furnaces  accessible  for  scaling 
and  repairs.  But  so  far  none  of  these  devices  has  proved  perfectly  satisfactory,  so 
that  the  method  of  securing  boiler-tubes  permanently  by  expanding  their  ends  con- 
tinues to  be  the  almost  universal  practice.  When  tubes  secured  in  this  manner  have  to 
be  removed  the  diameter  of  the  expanded  ends  is  reduced  by  closing  them,  and  even 
then  considerable  force  is  often  required  to  draw  the  tubes.  The  ends  of  iron  tubes 
generally  crack  during  this  process,  and  brass  tubes  are  so  much  injured  about  the  ends 
that  these  have  to  be  cut  off  and  new  ends  have  to  be  brazed  on. 

To  render  boiler-tubes  more  easily  removable  after  scale  has  formed  on  them  they 
are  often  made  tapering,  the  outside  diameter  at  the  front  end  being  sometimes  £  inch 
larger  than  at  the  back  end. 

The  following  method  is  said  to  have  been  successfully  used  in  France  with  iron 
tubes  :  A  short  piece  of  tube  made  of  very  soft  iron,  and  having  the  fibres  running  cir- 
cumferentially  instead  of  longitudinally,  is  welded  to.  the  ends  of  the  boiler-tubes  ;  these 
are  secured  in  the  tube-plates  by  expanding  them  and  turning  over  slightly  the  extreme 
projecting  ends.  When  a  tube  is  to  be  removed  the  ends  are  grasped  and  closed  by 
suitable  nippers ;  this,  it  is  said,  can  be  done  without  injuring  the  tube-ends  perma- 
nently, on  account  of  their  peculiar  structure. 

Figure  1,  Plate  XXII.,  represents  a  removable  tube  used  in  some  boilers  built  at 
the  West  Point  Foundry,  Cold  Spring,  N.  Y.,  in  1878.  The  tubes  are  4  inches  in  dia- 
meter and  13  feet  long  ;  the  ends  of  the  tubes  are  thickened  by  brazing  or  welding  upon 
them  a  coned  ring  ;  the  largest  diameter  at  the  back  end  is  made  a  little  smaller  than 
the  smallest  diameter  at  the  front  end.  The  tubes  are  driven  tightly  into  the  holes  of 
the  tube-plate  and  slightly  expanded.  The  tube-plates  are  one  inch  thick,  and  were 
turned  down  at  the  rim  to  a  thickness  of  £  inch  to  turn  the  flange.  The  holes  for  the 
tubes  were  punched,  and  reamed  in  place  after  the  tube-plates  were  riveted  to  the  shell. 
The  tube-plates  are  tied  together  by  braces  of  l£-inch  round  iron,  secured  by  nuts  and 
placed  about  18  inches  apart.  The  boilers  were  tested  with  cold  water,  and  found  to  be 
tight  under  a  pressure  of  135  pounds  per  square  inch.  These  tubes  are  known  as 
PaukscK  s  boiler-tubes,  and  have  been  used  to  some  extent  in  England  and  France. 

Figures  2,  3,  4,  Plate  XXII.,  represent  methods  of  securing  removable  tubes  used  in 
the  French  navy,  and  known  there  respectively  as  the  Systeme  Infernet  et  Gouttes 
(figure  2),  Systeme  Toscer  (figure  3),  and  Systeme  Langlois  (figure  4).  In  the  latter 


SEC.  9.  FLUES  AND  TUBES.  277 

the  front  end  of  the  tubes  is  packed  by  a  leaden  washer,  a  small  gutter  being  cut  in 
both  collar  and  plate,  into  which  the  lead  is  squeezed  by  screwing  up  the  tubes ;  a 
brass  collar  is  brazed  to  the  end  and  notched  for  the  purpose  of  applying  the  wrench. 
To  prevent  the  adhesion  of  the  tubes  by  rusting  the  threads  are  smeared  with  zinc 
cement,  and  it  has  been  found  that  tubes  can  be  taken  out  without  much  difficulty  after 
having  been  in  use  two  years.  The  back  end  is  fixed  by  means  of  a  slightly  conical 
steel  or  iron  ferrule,  tightened  by  means  of  an  expanding-tool.  It  is  claimed  that  a  tube 
can  be  removed  in  five  minutes. 

Figure  o,  Plate  XXII.,  represents  a  method  of  fixing  removable  tubes  which  was 
tried  some  years  ago  in  high-pressure  boilers  of  United  States  naval  vessels,  but  proved 
unsuccessful.  The  bushings  which  secure  the  brass  tubes  in  the  tube-plates  were  made 
of  composition  metal ;  those  at  the  back  end  of  the  tubes  were  soon  burnt  by  the  intense 
heat  prevailing  in  the  back-connection,  and  even  those  at  the  front  end,  which  were  not 
injured  by  heat,  could  not  be  unscrewed  after  the  boilers  had  been  in  use  a  short  time, 
but  were  twisted  off  in  the  attempt.  Similar  devices  have  been  tried  in  English  boilers 
with  equally  unsatisfactory  results. 

9.  Experiments  on  the  Holding  Power  of  Boiler-tubes  secured  by  various 
Methods. — In  January,  1877,  a  series  of  experiments  were  made  at  the  Navy-Yard, 
Washington,  D.  C.,  under  the  direction  of  Chief  Engineer  William  H.  Shock,  U.S.N., 
on  the  holding  power  of  boiler-tubes  fixed  by  various  methods  employed  in  marine  and 
locomotive  engineering.  Each  tube  subjected  to  trial  had  its  ends  fixed  in  square 
pieces  of  plate  resembling  portions  of  tube-plates.  The  pull  was  applied  to  stirrups 
attached  by  nuts  to  cross-heads  which  bore  against  the  plates  (see  Plate  XXV.)  The 
cross-heads  were  made  in  halves  and  with  a  circular  opening  in  the  centre,  in  order  to 
enclose  the  tube  and  allow  the  pull  to  be  applied  exactly  in  the  direction  of  the  axis  of 
the  tube.  Plates  XXIII.,  XXIV.  illustrate  fully  the  methods  of  fastening  the  tubes 
and  the  appearance  of  the  specimens  after  the  trial,  and  contain  a  complete  tabulated 
record  of  the  results  of  these  experiments.  The  Rodman  testing-machine  was  used  in 
making  these  experiments. 

Plate  XXIII.  exhibits  the  results  of  forty-eight  experiments  made  with  brass  tubes 
having  an  external  diameter  of  2.5  inches  and  2.6  inches,  and  an  area  of  metal,  in  cross- 
section  of  0.9  and  1.33  square  inches  respectively.  The  tube-plates  were  of  iron,  and 
varied  in  thickness  from  f  inch  to  f  inch.  Both  the  Prosser  and  the  Dudgeon  tool 
were  used  in  expanding  the  tubes  ;  the  effects  of  beading  over  the  ends  and  of  driving 
ferrules  into  the  tube-ends  were  tested  xinder  different  conditions: 

A  comparison  of  the  results  obtained  with  tubes  No.  5  and  No.  6  shows  that  the 


278  STEAM  BOILERS.  CHAP.  XI. 

partial  turning-over  of  the  ends  of  the  tube  effected  by  the  Prosser  expander  does 
not  give  such  a  firm  hold  of  the  tube-plate  as  the  beading-over  by  hand  in  connec- 
tion with  the  action  of  the  Dudgeon  roller-expander.  The  tubes  secured  by  simple 
expansion  gave  way  by  being  drawn  through  the  plates,  while  the  ends  which  were 
beaded  over  generally  broke. 

The  effect  of  ferrules  in  increasing  the  holding  power  of  tubes  is  very  marked ; 
they  prevent  the  ends  from  collapsing  and  being  drawn  through  the  plates. 

The  tubes  secured  by  nuts  only,  screwed  on  the  outside  of  the  plates,  gave  way  by 
drawing  the  ends  through  the  nuts  without  stripping  or  otherwise  injuring  the  thread. 
When  iron  ferrules  were  used  in  connection  with  the  nuts  the  holding  power  of  the 
tubes  was  greatly  increased.  In  experiments  Nos.  15  and  16  the  tubes  gave  way 
by  tearing  through  the  thread  ;  but  in  experiments  Nos.  19  and  20  the  tubes  drew  from 
the  nuts  without  breaking,  like  the  unferruled  tubes. 

The  lowest  results  were  obtained  in  experiments  Nos.  21  and  22,  when  the  tubes 
were  simply  expanded  by  the  Dudgeon  tool  in  a  f -inch  plate,  without  being  beaded 
over  or  secured  by  ferrules,  the  resistance  being  7,650  Ibs.  and  5,850  Ibs.  respectively. 
It  will  be  seen  that  even  in  this  most  unfavorable  case  the  holding  power  of  the  tube 
was  greatly  in  excess  of  any  strain  which  would  be  occasioned  by  the  pressure  of  steam 
upon  the  portion  of  the  tube-plate  which  any  one  tube  would  have  to  support  in  a 
boiler. 

The  following  general  conclusions  drawn  from  the  results  of  these  trials  are  quoted 
from  an  article  in  Engineering,  Sept.  14,  1877,  where  an  account  of  these  experiments 
was  first  published — viz.  :  "  (1)  That  tubes  fixed  by  the  Dudgeon  expander  and  beaded 
over  have  a  considerably  stronger  hold  of  the  tube-plates  than  those  fixed  by  the 
Prosser  expander,  particularly  with  thin  tube-plates ;  (2)  that  if  the  tubes  are  not 
beaded  over  the  hold  afforded  by  the  Dudgeon  is  less  than  that  afforded  by  the  Prosser 
system  of  fixing ;  (3)  that  with  both  expanders  the  introduction  of  ferrules  adds  very 
materially  to  the  holding  power  of  the  tubes  ;  (4)  that,  on  the  whole,  the  effect  of  fer- 
rules is  with  the  Dudgeon  expander  proportionately  greater  in  thick  than  in  thin  tube- 
plates,  while  in  the  case  of  the  Prosser  expander  the  proportionate  increase  of  resistance 
afforded  by  the  introduction  of  ferrules  is  not  materially  affected  by  the  thickness  of 
the  tube-plates ;  (5)  that  iron  ferrules  are  more  efficient  than  those  of  brass ;  and  (6) 
that  the  employment  of  nuts  screwed  on  the  tubes  outside  the  tube-plates  is  not  of  any 
service  in  increasing  the  holding  power  unless  the  tubes  are  ferruled." 

Plate  XXIV.  exhibits  eighteen  experiments  made  with  iron  tubes  secured  in  iron, 
steel,  and  copper  tube-plates  by  various  methods  obtaining  in  locomotive  engineering. 


SEC.  9.  FLUES  AND  TUBES.  279 

Dudgeon's  tool  is  used  in  all  cases  in  expanding  these  tubes.  The  outside  diameter  of 
the  tubes  is  2$-  inches,  but  their  lower  end  is  in  every  case  reduced  by  swaging  to  2f 
inches,  and  is  fixed  in  a  copper  or  steel  plate,  respectively  f  inch  and  f  inch  thick  ;  the 
upper  end  is  fixed  in  every  case  in  an  iron  plate  ^  inch  thick. 

In  experiments  No.  1  to  No.  8  the  ends  of  the  expanded  tubes  were  beaded  or 
riveted  over,  and  in  every  case  fracture  took  place  by  breaking  the  riveted  end  off  the 
tube,  except  in  experiment  No.  8,  when  the  riveted  end  was  cracked  but  not  completely 
detached  from  the  tube,  and  was  pulled  through  the  plate.  This  took  place  also  in  ex- 
periments Nos.  9  and  10,  where  the  ends  were  only  partly  riveted  over.  It  is  important 
to  notice  that  in  experiments  Nos.  5,  6,  7,  and  8,  where  the  lower  tube-plate  was  of 
copper,  as  well  as  in  experiments  Nos.  1  and  2,  where  at  the  lower  end  a  thin  copper 
ring  was  inserted  between  the  tube  and  the  steel  plate,  the  fracture  took  place  invaria- 
bly at  the  upper  end ;  while  in  experiments  Nos.  3  and  4,  identical  with  experiments 
X(  is.  1  and  2  with  the  omission  of  the  copper  ring,  fracture  took  place  once  at  the  upper 
end,  fixed  in  an  iron  plate,  and  once  at  the  lower  end,  fixed  in  a  steel  plate. 

The  great  difference  in  the  strain  under  which  tube-ends  fixed  in  precisely  the  same 
manner  gave  way  indicates  that  the  method  of  riveting  over  iron  tubes  is  apt  to  injure 
the  metal,  although  for  these  experiments  all  the  tubes  were  carefully  fixed  by  the  same 
experienced  workman.  The  strains  at  which  rupture  took  place  in  the  first  ten  experi- 
ments ranged  from  29,050  in  tube  No.  1  to  17,300  Ibs.  in  tube  No.  6  ;  the  mean  breaking 
strain  for  these  ten  tubes  was  22,837.5  Ibs. 

In  experiments  No.  11  to  No.  18  the  tube-ends  were  not  riveted  over,  and  the  tubes 
gave  way  invariably  at  the  lower  end,  showing  that  their  holding  power  was  decreased 
by  diminishing  their  diameter  and  the  thickness  of  the  tube-plates  ;  experiments  Nos. 
8,  9,  and  10  indicate,  on  the  contrary,  that  when  the  ends  are  riveted  over  the  holding 
power  of  the  tube  is  not  influenced  perceptibly  by  a  slight  decrease  in  the  thickness  of 
the  plate  and  in  the  diameter  of  the  tube. 

Comparing  experiments  Nos.  11  and  12  with  Nos.  13  and  14,  it  will  be  noticed  that 
the  holding  power  of  the  tubes  is  more  than  doubled  by  the  insertion  of  ferrules.  Ex- 
periments Nos.  13  and  14  show  also  that  iron  tubes,  simply  expanded  by  Dudgeon's 
process,  possess  more  than  sufficient  holding  power  to  bear  any  strain  which  may  be 
thrown  on  the  tube-plates  by  the  steam-pressures  used  in  locomotive  boilers. 

In  experiments  Nos.  15, 16, 17,  and  18  the  holes  were  made  tapering.  In  the  former 
two  experiments  the  larger  diameter  of  the  holes  was  ^  inch  greater  than  the  smaller 
diameter,  and  the  results  show  a  remarkable  decrease  in  the  holding  power  of  the  tubes 
from  that  of  the  tubes  Nos.  13  and  14,  with  simply  expanded  ends  in  cylindrical  holes. 


280  STEAM  BOILERS.  CHAP.  XI. 

In  experiments  Nos.  17  and  18  the  larger  diameter  of  the  taper  holes  was  -fr  inch  greater 
than  the  smaller  diameter,  and  with  these  proportions  the  holding  power  was  greatly 
increased. 

1O.  Sectional  or  Water-tube  Boilers,  Hanging  Tubes,  Double  Tubes,  etc. 

— Since  a  number  of  years  the  so-called  sectional  or  water-tube  boilers  have  come  into 
great  favor  as  stationary  boilers  for  various  purposes,  and  many  devices  relating  to  this 
class  of  steam-generators,  and  presenting  more  or  less  novelty,  have  been  patented  and 
introduced  into  the  market.  In  general  these  boilers  consist  of  an  assemblage  of  tubes 
connected  with  one  another  by  means  of  elbows  or  branch-pipes,  and  placed  in  vertical 
and  horizontal  tiers,  over  and  surrounding  a  grate,  and  enclosed  by  walls  built  of  fire- 
brick or  constructed  of  some  other  non-conducting  material ;  in  some  arrangements  the 
tubes  are  bent  into  a  coil  or  into  a  siphon-shape. 

The  principal  advantages  claimed  for  this  class  of  boilers  are  the  following :  (1)  The 
small  diameter  of  the  tubes  of  which  they  are  composed,  and  the  absence  of  riveted 
joints,  render  them  much  stronger  than  the  ordinary  rectangular  or  cylindrical  boilers. 
(2)  They  are  safer  ;  for  even  in  case  some  tubes  burst  no  violent  explosion  ensues,  be- 
cause the  fractured  parts  present  a  relatively  small  opening,  and  the  quantity  of  water 
and  steam  contained  in  these  boilers  is  small  in  proportion  to  their  power.  (3)  They 
can  be  cheaply  built,  and  repaired  with  great  facility,  duplicate  pieces  being  easily  kept 
in  store  for  this  purpose ;  the  separate  parts  of  a  boiler  can  be  transported  long  dis- 
tances without  great  expense  or  inconvenience ;  the  form  and  proportions  of  a  boiler 
are  easily  altered  or  adapted  to  any  available  space,  and  the  power  of  a  boiler  is  in- 
creased by  simply  adding  new  tiers  of  tubes  and  grate-surface.  (4)  Their  evaporative 
efficiency  can  be  made  equal  to  that  of  other  boilers,  and,  in  fact,  for  equal  proportions 
of  heating-surface  and  grate-surface,  it  is  often  somewhat  higher. 

With  two  or  three  exceptions  all  attempts  made  so  far  to  adapt  these  boilers  for  use 
on  board  of  vessels  have  resulted  unsuccessfully,  and  in  several  instances  disastrously. 
While  in  some  instances  these  failures  could  be  traced  to  avoidable  mistakes  in  the 
design  of  the  boilers,  there  are  several  reasons  why  tubulous  boilers  are  not  well  adapted 
for  marine  purposes,  unless  radical  changes  should  be  introduced  in  the  present  prac- 
tice of  marine  engineering. 

(1)  These  tubulous  boilers  occupy  as  much  valuable  space  as  the  ordinary  types  of 
marine  boilers. 

(2)  On  account  of  the  small  quantity  of  water  carried  in  them  any  irregularities  in 
the  supply  of  feed-water  or  in  the  management  of  the  fires  cause  sudden  fluctuations  of 
pressure,  and  a  sudden,  rapid  generation  of  steam  leads  to  an  accumulation  of  steam  in 


SEC.  10.  FLUBS  AND  TUBES.  281 

the  water-chambers,  and  to  priming,  loss  of  water,  and  overheated  tubes ;  these  trou- 
bles can  be  much  more  easily  avoided  with  regularly  and  continuously  working  factory 
engines  than  with  marine  engines,  which  have  often  to  be  operated  in  an  intermittent 
manner  in  getting  under  way  and  in  coming  to  a  wharf  or  to  an  anchorage. 

(3)  The  horizontal  or  inclined  water-tubes,  of  which  these  sectional  boilers  are 
mainly  composed,  do  not  present  a  ready  outlet  for  the  generated  steam.     The  steam- 
bubbles,  instead  of  being  able  to  follow  their  natural  tendency  and  rise,  have  generally 
to  travel  in  a  horizontal  direction  the  whole  length  of  the  tubes,  and  this  they  will  not 
do  without  being  urged  by  an  extraneous  force.     There  exists,  consequently,  a  liability 
for  steam  to  accumulate  in  the  water-tubes  and  cause  them  to  be  burnt;  and  this 
liability  is  generally  greater  in  the  case  of  marine  boilers,  where  economy  of  space  de- 
mands a  rapid  combustion  and  evaporation,  than  in  stationary  boilers,  where  economy 
of  fuel  is  sought  for  by  slow  combustion  and  evaporation. 

(4)  This  liability  to  overheating  of  the  tubes  is  still  increased  by  the  use  of  water 
which  forms  deposits  of  solid  matter  on  the  heating-surfaces  of  boilers.     The  surface- 
condensers  of  marine  engines  are  seldom  so  perfectly  tight  as  to  keep  the  boilers  fully 
supplied  with  distilled  water  for  any  length  of  time ;  and,  besides,  it  is  a  well-estab- 
lished fact  that  with  marine  boilers  the  choice  lies  between  the  formation  of  a  slight 
deposit  of  scale  and  rapid  corrosion. 

Some  inventors  have  relied  upon  the  scouring  action  of  the  water  circulating  rapidly 
through  the  tubes  of  their  boilers  as  a  means  of  preventing  the  deposit  of  scale ;  others 
thought  that  the  expansion  of  the  heated  tubes  would  detach  each  thin  deposit  of  scale, 
and  thus  prevent  it  from  accumulating  to  a  dangerous  extent.  But  these  speculations 
have  not  been  realized  in  practice.  Besides,  in  boilers  of  naval  vessels,  which  are  often 
kept  for  many  days  in  succession  under  banked  fires,  the  circulation  of  the  water  is 
during  such  time  necessarily  sluggish. 

In  PerJriwfs  tubulous  boiler,  which,  on  a  small  scale,  has  been  successfully  applied 
in  two  or  three  instances  to  marine  purposes,  distilled  water,  as  nearly  as  possible 
chemically  pure,  is  used.  All  joints  of  the  boiler  are  made  perfectly  tight.  A  surface- 
condenser  and  stuffing-boxes  of  peculiar  design  are  used  for  the  engines,  in  order  to 
avoid  all  loss  of  steam  ;  no  lubricant  is  used  for  the  valves  or  pistons  ;  the  whistle,  the 
blast,  and  the  steam-pumps  are  supplied  with  steam  by  an  auxiliary  boiler;  in  this 
manner  it  is  made  possible  to  use  the  same  pure  water  over  and  over  again.  A  quantity 
of  fresh  water  carried  in  tanks,  and  a  distiller,  are  provided  to  replace  any  water  acci- 
dentally lost. 

The  boiler  illustrated  in  figure  1,  Plate  XXVI.,  is  described  by  the  inventor, 


282  STEAM  BOILERS.  CHAP.  XL 

L.  Perkins,  in  a  lecture  delivered  before  the  Royal  United  Service  Institute,  1877,  as 
follows : 

"  The  horizontal  tubes  are  2J  inches  internal  and  3  inches  external  diameter,  except- 
ing the  steam-collecting  tube,  which  is  4  inches  internal  and  5£  inches  external  diame- 
ter. The  horizontal  tubes,  being  welded  up  at  each  end  one-half  inch  thick,  are  con- 
nected by  small  vertical  tubes  |  inch  internal  and  1^  inches  external  diameter.  The 
fire-box  is  formed  of  tubes  bent  into  a  rectangular  shape,  placed  at  a  distance  of  If 
inches  apart,  and  connected  by  numerous  small  vertical  tubes.  The  body  of  the  boiler 
is  made  of  a  number  of  vertical  sections  composed  each  of  eleven  tubes,  connected  at 
either  end  by  a  vertical  tube ;  these  sections  are  connected  at  both  ends  by  a  vertical 
tube  to  the  top  ring  of  the  fire-box,  and  by  another  to  the  steam-collecting  tube.  The 
whole  of  the  boiler  is  surrounded  by  a  double  casing  of  thin  sheet-iron,  filled  up  with 
vegetable  black  to  avoid  loss  of  heat.  Every  tube  is  separately  proved  by  hydraulic 
pressure  to  4,000  Ibs.  on  the  square  inch,  and  the  boiler  complete  to  2, 000  Ibs.,  this 
pressure  remaining  on  for  some  hours."  The  connecting-tubes  are  screwed  into  the 
main  tubes,  and  the  threads  are  then  calked  down  to  make  the  joint  perfectly  tight. 

Some  boilers  of  this  description  have  been  used  on  land  for  thirteen  years,  with  pres- 
sures varying  from  250  to  300  Ibs.,  and  tubes,  cut  out  for  examination  at  the  end  of 
that  period,  have  been  found  to  be  clean  and  to  show  no  signs  of  corrosion,  owing  partly 
to  the  rigorous  use  of  distilled  fresh  water,  and  partly,  it  is  supposed,  to  the  formation 
of  the  black  oxide  of  iron  by  the  contact  of  superheated  steam  with  the  highly-heated 
surfaces.  It  is  stated  that  steam  is  formed  even  in  the  lowest  tubes  ;  that  water  exists 
in  the  form  of  spray  in  the  middle  portion  of  the  boiler,  and  that  the  upper  tubes  con- 
tain dry  steam  ;  and  that  the  safety  of  the  tubes  is  ensured  by  the  great  density  of  the 
steam,  which  increases  greatly  its  power  of  conducting  heat.  These  boilers  have  gene- 
rally been  operated  with  a  low  rate  of  combustion,  while,  at  the  same  time,  the  ratio  of 
heating-surface  to  grate-surface  is  large. 

Figure  1,  Plate  XXVI.,  represents  one  of  the  four  boilers  of  the  steam-yacht  Wan- 
derer. Each  boiler  contains  19  square  feet  of  grate-surface  and  760  square  feet  of  heat- 
ing-surface ;  the  working  pressure  is  400  Ibs.  per  square  inch.  The  total  weight  of  the 
four  boilers,  including  water,  is  about  34  tons.  It  is  claimed  that  the  Wanderer's 
engines  developed,  with  92  revolutions  per  minute,  a  maximum  of  907  horse-powers. 
In  other  vessels,  having  boilers  of  identical  design  and  dimensions,  a  performance  of  150 
horse-powers  per  boiler  was  obtained. 

Figure  2,  Plate  XXVI.,  represents  a  Howard  water '-tube  boiler  designed  for  marine 
purposes.  The  tubes  forming  each  vertical  tier  communicate  with  each  other  at  one 


SEC.  10.  FLUES  AND  TUBES.  283 

» 

end  by  a  stand-pipe,  and  near  the  other  end,  which  is  closed,  by  short  corrugated  con- 
necting-tubes. The  closed  ends  are  provided  with  mudhole-doors.  The  feed-water 
enters  a  horizontal  tube  at  the  back  of  the  boiler,  connected  by  short  branches  to  the 
vertical  stand-pipes.  A  cylindrical  steam-drum  runs  across  the  top  of  the  boiler,  being 
connected  to  the  top  tube  of  each  vertical  tier. 

The  Belleville  water-tube  boilers  have  attracted  much  attention  in  France,  and  a 
great  number  of  them  were  built  some  years  ago  for  the  French  navy.  Various  modifi- 
cations have  been  introduced  in  these  boilers  from  time  to  time.  Figure  2,  Plate 
XXVII.,  represents  a  boiler  of  this  class  built  for  the  despatch- vessel  IS  Active,  of  the 
French  navy,  in  1868.  There  were  three  of  these  boilers,  supplying  steam  to  compound 
engines  of  400  indicated  horse-powers. 

The  following  information  regarding  them  is  derived  from  Engineer  ing, March  4,1870 : 
Each  steam-generator  proper  consists  of  eleven  "elements,"  each  composed  of 
twelve  tubes,  disposed  one  above  the  other  and  coupled  at  their  alternate  ends  by  con- 
necting-boxes. The  eleven  elements  are  placed  side  by  side  at  a  short  distance  apart. 
A  transverse  tube,  B,  connects  all  the  lower  tubes  and  serves  to  distribute  the  feed- 
water  to  the  various  elements.  The  upper  tubes  are  all  connected  with  a  transverse 
steam-collecting  tube,  C,  parallel  to  which  is  placed  the  round  pipe  D,  which  serves  to 
lead  the  steam  off  to  the  engines.  The  pipes  C  and  D  are  connected  by  five  vertical 
pipes  of  different  sizes,  for  the  purpose  of  equalizing  the  draught  of  steam  from  the 
various  sections.  The  tubes  are  of  wrought-iron,  lap- welded;  the  connecting-boxes 
into  which  the  tubes  are  screwed  are  of  malleable  cast-iron,  and  each  is  furnished  with  a 
couple  of  mudholes  opposite  the  ends  of  the  tubes.  All  the  elements  are  connected  to- 
gether at  the  front  by  the  upper  and  lower  connecting-tubes,  and  at  the  back  by  a 
wrought-iron  frame  and  tie-bolts,  distance-pieces  being  provided  to  maintain  the  proper 
intervals  between  the  elements  ;  in  this  manner  the  tubes  are  left  free  to  expand  or  con- 
tract longitudinally.  The  tubes  are  each  formed  in  a  single  piece,  except  the  upper  and 
lower  tubes  of  each  element,  which  are  each  made  in  two  pieces,  connected  by  a 
coupling,  for  the  purpose  of  facilitating  the  putting  together  and  taking  to  pieces  of  the 
elements.  The  whole  of  the  boiler  proper  is  enclosed  in  a  casing  composed  of  wrought- 
iron  plates  and  angle-irons,  lined  with  fire-bricks.  A  number  of  plates  are  placed  in 
the  upper  part  of  the  boiler  to  deflect  the  current  of  the  gases.  The  feed  is  regulated 
by  a  self-acting,  adjustable  float  placed  in  the  vertical  wrought-iron  cylinder  in  front  of 
the  boiler,  to  which  also" the  gauge-cocks  are  attached.  A  "separator,'''  placed  between 
the  boilers  and  the  engines,  frees  the  steam  of  the  water  and  other  foreign  matter  held 
in  suspension.  The  principal  dimensions  of  the  boilers  of  IS  Active  are  as  follows : 


284  STEAM  BOILERS.  CHAP.  XI. 

Number  of  boilers 3. 

Height  of  boilers 7  feet  7  inches 

Length  of  boilers 8  feet  f  inch. 

Width  across  three  boilers 14  feet  8  inches. 

Total  number  of  tubes  396. 

Interior  diameter  of  tubes 2f  inches. 

Thickness  of  tubes  0.24  inch. 

Length  of  tubes 6  feet  lOf  inches. 

Total  grate-surface 75.34  square  feet. 

Total  heating-surface 2,347  square  feet. 

Load  on  safety-valves 113  Ibs.  per  square  inch. 

Figure  1,  Plate  XXVII.,  represents  the  HerresJioff  coil-boiler  of  the  steam-yacht 
Estelle. 

The  following  data  are  derived  from  the  report  of  the  Board  of  Naval  Engineers,  who 
conducted  a  trial  with  this  vessel  in  December,  1877 : 

This  boiler  consists  of  a  single  circular  grate,  7  feet  in  diameter,  surrounded  by  a 
fire-brick  wall  18  inches  in  height  above  the  top  of  the  grate-bars  and  7  inches  in  thick- 
ness. Upon  the  top  of  this  brick  wall  there  rests  a  single  coil  of  continuous  wrought- 
iron  pipe,  which  contains  the  steam  and  water,  while  its  outside  is  exposed  to  the  hot 
gases  of  combustion.  The  outline  of  this  coil,  considered  as  a  whole,  is  composed  of 
the  frustums  of  two  right  cones,  one  superimposed  upon  the  other.  The  lower  frustum 
is  7  feet  in  inner  diameter  at  the  base  and  6  feet  in  inner  diameter  at  the  top,  with  a 
vertical  height  of  7  feet  and  4  inches.  The  upper  frustum  is  6  feet  in  inner  diameter  at 
the  base  and  1  foot  and  11  inches  in  inner  diameter  at  the  top,  with  a  vertical  height  of 
lOf  inches.  The  spirals  of  the  lower  frustum  are  kept  apart  f  inch  by  stirrup-bolts. 
The  spirals  in  the  upper  frustum  touch,  and  the  entire  top  is  covered  with  sheet-iron ; 
thus  all  the  gases  are  compelled  to  pass  between  the  openings  between  the  spirals  of  the 
lower  frustum.  The  coil  makes  a  total  of  thirty  turns,  all  of  which  are  continuous, 
without  a  single  joint,  being  made  by  welding  together  the  ends  of  the  several  sections 
of  pipe  composing  the  coil.  Starting  from  the  bottom,  the  pipes  forming  the  coil 
gradually  decrease  in  size,  the  lowest  section  being  4|  inches  in  outside  diameter  and 
0.119  inch  in  thickness,  and  the  uppermost  section  being  If  inches  in  outside  diameter 
and  0.069  inch  in  thickness.  The  coil  is  surrounded  by  a  hollow  cylindrical  casing, 
8  feet  3  inches  in  outside  diameter,  filled  with  fire-brick  If  inches  thick. 

The  feed-water  enters  the  coil  at  the  extreme  top,  and,  flowing  slowly  down  the 


SEC.  10.  FLUES  AND  TUBES.  285 

• 

spirals,  becomes  converted  into  steam.  From  the  lower  end  of  the  coil  a  straight 
wrought-iron  pipe,  4|  inches  in  outside  diameter,  passing  up  on  the  coil  directly  over 
the  grate,  leads  the  steam  to  the  "separator"  a  cylindrical  vessel  located  outside  the 
boiler,  where  the  water  and  other  impurities  mingled  with  the  steam  are  deposited. 
The  steam  is  drawn  off  at  the  top  of  the  separator,  and  passes  through  a  coil  of  pipe 
within  the  uptake  of  the  boiler,  where  it  is  superheated  before  it  enters  the  engines.  It 
is  essential  that  a  portion  of  the  feed-water  should  pass  in  the  form  of  spray  with  the 
steam  into  the  separator,  in  order  to  prevent  the  overheating  of  the  lower  coils  of  the 
tube.  In  the  older  boilers  of  .this  type,  in  which  sea-water  was  used,  this  surplus  of 
water  entered  the  separator  as  highly-concentrated  brine,  and  was  blown  off.  In  later 
boilers,  where  fresh  water  is  used,  this  water  is  either  blown  into  the  condenser  or  is 
directly  fed  back  into  the  boiler  by  a  special  pump.  The  quantity  of  water  which 
passes  thus  into  the  separator  is  about  25  per  cent  of  the  quantity  evaporated. 

The  following  are  the  principal  dimensions  and  proportions  of  the  boiler  illustrated 
on  Plate  XXVII. : 

Diameter  of  the  boiler  to  outside  of  casing 8  ft.  3  ins. 

Height  of  the  boiler  from  bottom  of  ashpit  to  top  of  coil 11  ft.  3  ins. 

Area  of  grate-surface 38.4846  sq.  ft. 

Total  area  of  heating-surface,  measured  on  the  outside  of  the  pipe  511.184  sq.  ft. 

Length  of  the  axis  of  the  coil 539.550  ft. 

Capacity  of  the  coil 34.488  cub.  ft. 

Ratio  of  heating-surface  to  grate-surface 13.283  to  1. 

Weight  of  brick- work  in  the  boiler  (calculated) 7,250  Ibs. 

Weight  of  iron  in  the  boiler  (calculated) 9,250  Ibs. 

Total  weight  of  boiler,  including  brick- work,  grate-bars,  ashpit, 

uptake,  separator,  casing,  coil,  etc 16,500  Ibs. 

Weight  of  water  in  coil  and  separator,  allowing  the  coil  to  be  half- 

filled 1,100  Ibs. 

Steam  was  raised  with  wood  from  water  at  the  temperature  of  44°  Fahr.  in  sufficient 
quantity  to  start  the  motive-engine,  and  maintain  it  in  motion,  in  seven  minutes  from 
the  lighting  of  the  fire.  The  feeding  has  to  commence  a  few  moments  before  the  fires 
are  lighted. 

During  the  trial,  which  lasted  eight  hours,  the  extreme  variations  of  boiler-pressure 
were  between  65  and  75  Ibs.  per  square  inch.  This  uniformity  of  pressure  is  ascribed  to 
be  due  to  the  use  of  artificial  draught  by  means  of  a  fan-blower,  and  to  the  uniform 
working  of  the  engine. 


286  STEAM  BOILERS.  CHAP.  XI. 

• 

During  a  short  full-power  trial,  lasting  fifteen  minutes,  the  engine  developed  293.28 
indicated  horse-powers,  with  a  steam-pressure  of  106.5  Ibs.  in  the  boiler. 

The  interior  of  the  pipe  is,  of  course,  utterly  inaccessible  for  scaling  or  examination. 
The  use  of  the  boiler  is  limited  to  fresh  water,  supplied  by  tanks  or  surface-condensers. 
When  sea- water  is  used  the  coil  gradually  scales  up,  commencing  at  the  lower  end  of 
the  coil. 

The  lightness  of  the  boiler  is  dependent  to  a  great  extent  upon  the  small  amount  of 
heating-surface  and  to  the  thin  walls  of  the  fire-brick  casing ;  but,  even  after  increasing 
the  former  to  the  amount  usual  in  marine  boilers,  the  weight  of  the  Herreshoff  boiler 
would  be  only  about  one-half  of  the  weight  of  the  ordinary  marine  boiler. 

Many  novel  devices  in  the  arrangement  and  form  of  the  tubes  of  vertical  boilers  have 
been  introduced  of  late,  with  a  view  to  combining  lightness  and  compactness  and  rapid 
circulation  of  the  water  in  every  part  of  the  boiler  with  high  potential  and  economic 
evaporative  efficiency. 

The  Davey-Paxman  boiler,  illustrated  in  figure  2,  Plate  XXVIII.,  is  highly  recom- 
mended in  these  respects.  The  merits  of  this  boiler  are  due  to  the  bent  and  tapering 
water- tubes  and  to  the  deflector  inserted  in  the  top  of  each  tube.  The  water  in  these 
tubes,  being  exposed  to  the  full  heat  of  the  furnace,  soon  acquires  a  high  temperature, 
and  as  it  rises  rapidly  it  is  replaced  by  solid  water  flowing  in  at  the  lower  end.  So 
great  is  the  velocity  of  the  water  through  these  tubes  that  it  rises  in  jets  up  to  the 
crown-plate,  unless  arrested  by  the  deflectors,  which  divert  these  water-jets  downward 
and  keep  the  water  perfectly  smooth  on  the  surface.  This  rapid  circulation  of  the  water 
allows  no  incrustation  to  take  place  in  the  tubes. 

In  many  cases  boilers  are  fitted  with  so-called  "  hanging-tubes."  These  tubes  hang 
vertically  over  the  fire,  being,  closed  at  the  bottom  by  means  of  a  plug  or  by  welding,  and 
being  secured  at  the  upper  end  in  the  tube-plate  which  forms  the  crown-plate  of  a  very 
high  furnace.  A  tube  of  smaller  diameter  leads  down  into  the  larger  tube,  leaving  an 
annular  space  through  which  the  steam  ascends,  while  solid  water  flows  down  through 
the  inner  tube.  The  top  of  the  latter  extends  a  short  distance  above  the  outer  tube, 
but  the  lower  end  does  not  reach  quite  to  the  bottom  of  the  outer  tube,  in  order  to  leave 
room  for  the  passage  of  the  water.  The  success  of  this  arrangement  depends  on  the 
complete  separation  of  the  ascending  and  descending  currents  in  the  tubes.  The  outer 
tubes  are  sometimes  fitted  at  the  top  with  deflecting  arrangements  of  various  forms. 
These  hanging-tubes  are  principally  used  in  the  boilers  ^of  fire-engines,  road-en- 
gines, etc. 


CHAPTER   XII. 

UPTAKE,    CHIMNEY,    STEAM-JETS,    FAN-BLOWEBS,   ETC. 

1.  Smoke-connections  and  Uptake. — The  gases  of  combustion  are  discharged 
by  the  tubes  or  flues  into  chambers  called  the  smoke-connections,  or,  in  the  return-tube 
boiler,  the  front-connections,  which  gradually  converge  to  a  common  passage,  called  the 
uptake,  leading  to  the  base  of  the  chimney.  The  smoke-connections  and  uptake  are 
either  built  permanently  within  the  shell  of  the  boiler,  forming  an  integral  part  of  the 
latter  and  being  partly  surrounded  by  water  and  steam-spaces,  or  they  consist  of  a 
separate  box,  constructed  of  angle-irons  and  plate-iron,  and  secured  to  the  outside  of 
the  shell  of  the  boiler.  In  the  former  case  the  uptake  may  be  so  arranged  as  to  present 
valuable  heating-surface  for  drying  and  superheating  the  steam ;  this  subject  will  be 
considered  in  chapter  xiii.  When  the  front-connections  and  uptake  are  built  sepa- 
rately they  form,  with  their  linings,  a  considerable  part  of  the  total  weight  of  the  boil- 
ers ;  they  increase  greatly  the  temperature  of  the  fire-room  by  radiation,  unless  they  are 
well  protected  by  non-conductive  materials ;  and  they  give  frequently  trouble  by 
warping  when  the  gases  of  combustion  are  discharged  at  a  high  temperature. 

The  smoke-connections  must  not  only  form  a  sufficiently  large  and  unobstructed  pas- 
sage for  the  gases  of  combustion,  but  must  allow  easy  access  to  be  had  to  the  tubes  for 
sweeping,  replacing,  or  calking  them ;  for  this  purpose  they  are  provided  with  large 
hinged  doors.  The  cross-area  of  the  front-connections  increases  gradually  from  the 
bottom  to  the  top  and  from  the  ends  of  the  boiler  to  the  place  where  they  merge  in  the 
uptake,  so  as  to  preserve  a  uniform  ratio  of  cross-area  to  the  bulk  of  the  gases  dis- 
charged into  them  by  each  additional  row  of  tubes.  All  sudden  enlargements  should 
be  avoided  as  much  as  possible  ;  all  bends  should  be  made  with  easy  curves,  and  the 
irregular  form  of  the  uptake  should  change  gradually  into  the  regular  figure  represent- 
ing the  cross-section  of  the  smoke-pipe.  When  several  currents  of  a  fluid,  moving  in 
different  directions,  meet  in  a  common  passage  they  retard  each  other,  and,  under  cer- 
tain conditions,  the  one  moving  with  the  greatest  speed  may  even  obliterate  entirely 


287 


288  STEAM  BOILERS.  CHAP.  XIL 

the  other  currents.  This  well-known  phenomenon  is  too  often  lost  sight  of  in  the  con- 
struction of  the  uptakes  of  boilers,  and  the  draught  of  boilers  may  be  seriously  injured 
in  consequence.  The  current  of  gases  issuing  from  one  set  of  flues  should  never  cross  the 
direction  of  other  currents  on  entering  the  same  passage,  but  partitions  should  be  pro- 
vided which  keep  the  currents  separate  till  they  have  assumed  the  same  direction. 

In  rectangular  boilers  of  the  return-tube  type  the  front  smoke-connections  and  the 
uptake  are  generally  built  permanently  in  the  boiler  (see  Plates  VI.,  VII.,  XVII.)  In 
this  case  the  front  tube-plates  are  set  back  a  short  distance  from  the  front  of  the  boiler, 
and  the  latter  is  made  to  slope  outward  from  the  bottom  of  the  front-connection  up- 
ward, in  order  to  get  more  room  at  the  top  for  the  passage  of  the  gases.  The  bottom  of 
the  connection  must  be  placed  so  as  to  give  sufficient  room  for  expanding  and  calking 
the  lower  row  of  tubes,  and  for  turning  the  flange  which  connects  the  tube-plate  to  the 
bottom  plate  of  the  connection.  Room  is  saved  between  the  latter  and  the  furnace- 
crown  by  turning  the  flange  on  the  tube-plate,  and  not  on  the  bottom  plate  of  the  front- 
connection.  The  top  of  the  front-connection  is  generally  arched,  not  only  to  give  it 
strength,  but  because  such  a  form  offers  less  resistance  to  the  flow  of  the  gases  than  a 
square  cross-section. 

The  front-connections  form  often  a  clear  passage  extending  from  one  end  of  the 
boiler  to  the  other.  In  this  case  the  construction  of  the  boiler  is  greatly  simplified  by 
leaving  the  whole  front  of  the  connections  open,  and  forming  the  jambs  or  supports  for 
the  connection-doors  by  bolting  flat  bars  to  the  front  of  the  boiler  across  this  open 
space. 

In  the  rectangular  boilers  of  United  States  naval  vessels  these  jambs  are  generally 
formed  by  columnar  water-spaces  (see  Plates  VI.,  VII.) ;  they  complicate  the  con- 
struction of  this  part  of  the  boiler,  but  are  useful  as  channels  for  the  downward  course 
of  the  water. 

By  extending  these  water-spaces  across  the  front-connections,  so  as  to  form  walls 
which  separate  the  several  nests  of  tubes,  the  weight  of  the  boiler  is  slightly  increased, 
but  some  additional  heating-surface  and  freer  channels  for  the  circulation  of  the  water 
are  gained ;  and  the  draught  of  the  end  furnaces  is  improved,  because  the  body  of 
gases  generated  by  each  furnace  is  kept  separate  until  the  different  currents  assume  the 
same  direction  on  entering  the  uptake. 

The  form  of  the  uptake  depends  on  the  arrangement  of  the  boilers  with  reference  to 
one  another  and  to  the  chimney.  When  a  single  boiler  is  used  the  uptake  slopes  in- 
ward, so  as  to  bring  the  smoke-pipe  over  the  base  of  the  boiler.  When  several  boilers 
are  placed  opposite  to  one  another  the  uptake  slopes  outward,  spanning  the  space  be- 


SBC.  1.  UPTAKE,  CHIMNEY,  STEAM-JETS,  FAX-BLOWERS,  ETC.  289 

tween  the  boilers ;  with  such  an  arrangement  each  boiler  contains  a  portion  of  the 
uptake,  so  that  when  the  boilers  are  placed  in  position  the  sides  of  the  overhanging 
uptake  meet  and  are  bolted  together,  forming  thus  a  common  passage  (see  Plates  VI., 
VII.)  In  such  a  case  it  would  be  better  to  keep  the  uptake  of  each  boiler  separate  by 
a  partition  extending  to  the  base  of  the  chimney.  Such  parts  of  the  uptake  as  lie  out- 
side the  shell  of  the  boiler,  and  are  not  surrounded  by  steam-drums,  are  frequently 
lined  with  fire-brick,  or  are  coated  on  the  outside  with  some  incombustible,  non-con- 
ductive material  to  prevent  the  radiation  of  heat. 

With  high-pressure  cylindrical  boilers  it  is  more  convenient  to  build  the  boiler 
proper  complete  in  itself,  and  to  add  the  front-connections  and  uptake  as  separate 
structures ;  this  plan  simplifies  the  construction  of  the  cylindrical  shell  and  avoids  the 
use  of  flat  stayed  surfaces.  The  bottom,  top,  and  sides  of  the  uptake  and  connections 
are  generally  either  lined  with  fire-brick  or  are  made  with  a  double  shell,  which  is  fre- 
quently filled  with  some  non-conductive  substance,  like  plaster-of -Paris  or  a  mixture  of 
plaster-of -Paris  and  ashes. 

The  uptakes,  and  the  fastenings  which  secure  them  to  the  boilers,  must  be  strong 
enough  to  carry  the  weight  of  the  smoke-pipe  in  addition  to  their  own  weight ;  and, 
besides,  they  are  sometimes  designed  to  tie  the  boilers  together  at  the  top.  They  are 
made  to  rest  partly  on  the  top  of  the  cylindrical  shell,  and  special  provisions,  in  the 
shape  of  beams  and  stanchions,  are  often  made  to  support  their  overhanging  portions. 
The  required  strength  and  stiffness  of  the  structure  should  be  provided  for  by  a  proper 
arrangement  of  the  frames,  made  of  angle-irons,  T-irons,  or  channel-irons.  The  selec- 
tion of  the  thickness  of  the  plate-iron  must  be  governed  by  the  following  considera- 
tions :  It  must  be  riveted  together  with  air-tight  joints  ;  it  must  not  buckle  under  the 
strains  or  warp  in  consequence  of  the  heat  to  which  it  is  exposed  ;  and  it  must  not  be 
destroyed  too  rapidly  by  corrosion.  For  double  shells  much  thinner  iron  may  be  used 
than  for  single  shells  lined  with  fire-brick.  The  inner  lining  of  double  shells  is  made 
heavier  than  the  outer  lining,  because  it  is  more  exposed  to  warping  and  corrosion. 

In  the  boilers  of  the  U.  S.  S.  Nipsic  (see  Plates  XXIX.,  XXX.)  the  front-connec- 
tions of  each  set  of  boilers  on  the  same  side  of  the  vessel  form  a  clear  passage  from  one 
extreme  end  to  the  other.  They  are  attached  to  the  front  of  the  boilers  by  angle-irons, 
and  to  the  cylindrical  shells  by  channel-irons,  secured  by  tap-bolts.  The  bottom  of  the 
front-connections  is  formed  by  a  single  thickness  of  plate  riveted  to  the  angle-iron, 
which  extends  in  one  continuous  length  along  the  fronts  of  the  boilers.  The  other 
walls  of  the  front-connections  and  of  the  uptake  are  double,  the  inner  lining  being 
made  of  No.  10  W.  G.  iron  and  the  outer  lining  of  No.  13  W.  G.  iron.  The  inner  and 


290  STEAM  BOILERS.  CHAP.  XII. 

outer  plates  of  the  double  shell  are  connected  by  channel-irons  (2J*  X  2"  X  f "),  through- 
rivets  passing  through  both  plates  and  both  flanges  of  the  channel-irons.  The  sides  of 
the  connections  and  uptake  are  connected  by  angle-irons.  Additional  supports  for  the 
connections  are  provided  in  the  shape  of  brackets  resting  on  the  flanges  of  the  furnace- 
tubes,  and  in  the  centre  under  the  smoke-pipe  the  uptake  is  supported  by  a  pair  of 
flanged  beams,  12  inches  deep,  running  in  the  fore-and-aft  direction  of  the  vessel. 
These  beams  are  placed  20  inches  apart,  and  are  supported  at  either  end  by  a  wrought- 
iron  stanchion  resting  on  the  keelson.  Supports  for  the  deck-beams  over  the  boilers 
rest  likewise  on  these  beams. 

The  weight  of  the  front-connections  and  uptake  of  these  boilers  is,  according  to  cal- 
culation, about  10,000  Ibs.,  and  the  actual  weight  of  the  plaster-of-Paris  used  in  filling 
them  was,  in  the  dry  state,  5,000  Ibs.,  making  the  total  weight  of  the  front-connections 
and  uptake  of  these  boilers  when  filled  about  16,350  Ibs. 

In  the  U.  S.  S.  Trenton,  having  eight  three-furnace  boilers  twelve  feet  in  diameter, 
each  boiler  has  a  separate  front-connection,  sloping  outward  from  a  least  width  of  9 
inches  at  the  bottom  to  a  uniform  width  of  30  inches  at  the  top,  where  it  is  open  to  the 
uptake.  The  latter  forms  a  continuous  passage  along  the  fronts  of  the  boilers  on  each 
side  of  the  vessel.  Its  cross-section  is  square,  and  its  width  and  height  increase  gradu- 
ally from  the  extreme  ends  to  its  junction  with  the  base  of  the  chimney.  All  the  walls 
of  the  connections  and  uptake  consist  of  a  single  shell,  lined  with  fire-brick  in  the  up- 
take. The  side,  bottom,  and  front  plates  of  each  front-connection  are  riveted  to  a  two- 
inch  angle-iron  bent  to  the  shape  required  for  the  outline  of  the  box  and  secured  to  the 
front  of  the  boiler,  and  to  the  square  frames,  made  of  2-inch  angle-irons,  surrounding 
the  connection-door  openings.  The  plates  forming  the  uptake  are  of  J-inch  iron,  con- 
nected by  2-inch  angle-irons.  The  uptake  is  fastened  at  the  back  to  the  cylindrical 
shell  of  each  boiler  by  means  of  a  3-inch  angle-iron,  and  the  overhanging  part  is  sup- 
ported by  4-inch  T-irons,  two  of  which  are  placed  on  the  top  of  the  front-connection  box 
of  each  boiler.  These  T-irons  extend  across  the  fire-room,  and  are  secured  at  either  end 
by  a  strap  bolted  to  the  front  of  the  boiler.  For  the  support  of  the  smoke-pipe  the 
central  part  of  the  uptake  forms  a  heavy  framework.  The  pipe  rests  on  a  square 
f-inch  plate,  with  a  circular  opening  corresponding  to  the  cross-section  of  the  smoke- 
pipe,  and  strengthened  by  a  ring  formed  of  4-inch  angle-iron  and  having  an  inner 
diameter  2  inches  larger  than  the  outside  diameter  of  the  base  of  the  pipe.  The  four 
sides  of  this  horizontal  top  plate  are  secured  by  3-inch  angle-irons  to  vertical  plates  f 
inch  thick.  The  vertical  plates  running  athwartships  are  12  inches  deep,  and  those 
running  in  a  fore-and-aft  direction  are  secured  to  the  cylindrical  shells  of  the  boilers  by 


SEC.  2.  UPTAKE,  CHIMNEY,  STEAM-JETS,  PAN-BLOWERS,  ETC.  291 

3-inch  angle-irons.  The  rest  of  the  uptake  is  connected  to  this  central  portion  by 
2-inch  angle-irons. 

It  is  of  the  utmost  importance  that  the  uptake-doors  be  made  to  fit  air-tight  against 
their  seats,  in  order  to  prevent  the  in-leakage  of  air,  the  effect  of  which  is  to  decrease 
the  draught  of  the  chimney  by  lowering  its  temperature  and  increasing  the  bulk  of 
gases  to  be  passed  through  it  in  a  given  time. 

The  draught  of  the  boiler  measures,  other  things  equal,  its  potential  vaporization ; 
and  having  constructed  a  boiler,  every  precaution  should  be  taken  to  obtain  from  it  the 
utmost  performance  by  losing  none  of  the  draught  due  to  the  temperature  and  bulk  of 
the  gases  of  combustion  delivered  into  the  base  of  the  chimney.  When  it  is  neces- 
sary to  force  from  a  boiler  the  utmost  quantity  of  steam  in  a  given  time,  the  uptake- 
doors,  where  they  meet  their  seat,  should  be  luted  with  clay,  so  as  to  absolutely  prevent 
the  ingress  of  the  cold  external  air.  These  remarks,  of  course,  apply  only  to  the  cases 
where  natural  draught  is  employed  alone  or  in  conjunction  with  a  steam-jet  in  the 
chimney.  When  the  draught  is  produced  artificially  by  means  of  blowers  delivering 
blasts  of  air  into  closed  ashpits,  tight  uptake-doors  may  still  be  needed  to  prevent  the 
gases  of  combustion  from  being  driven  into  the  fire-room. 

When  the  uptake-doors  are  so  large  that  the  labor  of  opening  and  closing  them  be- 
comes serious  it  is  frequently  convenient  to  construct  in  them  a  much  smaller  door,  to  be 
opened  when  it  is  desired  to  check  the  combustion  in  the  furnaces.  This  combustion 
may,  indeed,  be  checked  still  more  promptly  by  opening  the  furnace-doors,  thereby 
allowing  the  inrush  of  a  mass  of  cold  air  above  the  incandescent  fuel  and  through  the 
furnaces  and  tubes  ;  but  it  is  done  at  the  risk  of  injuring  the  riveting  by  the  too  sudden 
cooling  of  the  plates,  and  the  radiation  into  the  fire-room  from  the  glowing  fires  is  so 
great  as  to  be  a  serious  inconvenience,  and  sometimes  an  injury,  to  all  the  persons  who 
have  duties  there. 

2.  Forms  and  Dimensions  of  Chimneys. — The  chimneys  of  marine  boilers  are 
generally  cylindrical,  with  a  circular  cross-section.  Sometimes  the  cross-section  is  oval, 
with  the  greater  diameter  lying  in  the  fore-and-aft  direction  of  the  vessel.  This  form 
is  used  to  gain  room  on  deck  athwartships  for  clearing  certain  parts  of  the  rigging. 
Another  advantage  claimed  for  this  form — viz.,  that  it  offers  less  resistance  to  a  head- 
wind— is  practically  insignificant.  The  flat  sides  of  oval  chimneys  are  stiffened  by 
braces.  A  chimney  of  circular  cross-section  has  not  only  the  strongest  form,  requires 
the  least  weight  of  metal,  and  is  most  easily  made,  but  offers  the  least  surface  for  fric- 
tion and  radiation. 

When  several  boilers  discharge  their  gases  into  the  same  chimney  the  latter  is  some- 


292  STEAM  BOILERS.  CHAP.  XII. 

times  divided  by  partitions  running  the  whole  length  of  the  pipe,  so  that  each  division 
forms  a  separate  chimney  for  each  boiler.  This  arrangement  is  advantageous  for  war- 
vessels,  which  frequently  steam  with  only  a  fraction  of  their  boiler-power.  According 
to  Ledieu,  this  plan  of  subdividing  the  chimney  is  often  adopted  in  the  French  navy, 
even  when  hoisting-pipes  are  used,  although  in  such  cases  it  complicates  their  con- 
struction greatly. 

The  effect  of  this  division  of  a  chimney  by  partitions  extending  from  bottom  to  top 
was  tested  by  Chief  Engineer  Isherwood,  of  the  United  States  navy,  on  board  the 
United  States  steam-frigate  San  Jacinto,  in  1862.  .The  tubular  boilers  of  that  vessel 
were  two  in  number,  placed  opposite  each  other  with  the  fire-room  between  and  in  com- 
mon to  both,  the  chimney  being  also  common  to  both  and  placed  over  the  centre  of  the 
fire-room.  When  only  one  boiler  was  in  operation  the  difference  in  its  draught  was 
strongly  marked,  whether  the  partition  was  left  out  and  the  whole  chimney  cross-area 
used,  or  whether  the  partition  was  put  in  and  half  the  chimney  cross-area  used  ;  the 
ashpit-doors,  furnace-doors,  and  uptake-doors  of  the  boiler  out  of  operation  being  care- 
fully luted  in  the  former  case  so  as  to  absolutely  prevent  any  passage  of  air  through  it. 

When  the  draught  is  produced  by  artificial  means — viz.,  by  a  steam -jet  or  by  fan- 
blowers — there  is  a  certain  cross-area  of  chimney  which  gives  the  least  resistance  by 
friction  and  the  best  effect  of  the  blast,  while  the  height  of  the  chimney  need  only  be 
great  enough  to  discharge  the  products  of  combustion  without  producing  inconvenience. 
In  the  English  torpedo-vessel  Vesuvius  the  chimney  consists  of  a  horizontal  duct  leading 
aft  along  the  sides  of  the  vessel. 

When  natural  draught  is  to  be  used — that  is  to  say,  when  the  draught  is  to  be  pro- 
duced by  the  difference  in  weight  of  the  column  of  hot  gas  within  the  chimney  and  of 
an  equally  high  column  of  outside  air — the  dimensions  of  the  chimney  for  a  given  rate 
of  combustion  may  be  calculated  according  to  the  rules  and  formulae  given  in  section 
11,  chapter  ii.  When  natural  draught  is  used  in  marine  boilers  the  cross-area  of  the 
chimney  varies  from  one-sixth  to  one-tenth  of  the  area  of  the  grate  ;  and  the  limit 
of  the  height  of  the  chimney  of  steamships  is  about  65  feet,  measured  from  the  level  of 
the  grate. 

In  war-vessels  which  are  intended  to  manoeuvre  frequently  and  for  long  periods 
under  sail  without  the  use  of  steam-power  the  chimney  is  made  telescopic,  with  one  or 
two  movable  sections,  which  slide  within  a  fixed  pipe  and  are  hoisted  when  the  boilers 
are  in  use  and  lowered  after  the  fires  are  hauled.  The  chimneys  of  steam-launches  and 
similar  small  vessels  are  frequently  provided  with  a  hinge  (see  Plate  XVI.),  so  that  they 
can  be  let  down  into  a  horizontal  position. 


SEC.  2.  UPTAKE,  CHIMNEY,  STEAM-JETS,  FAN-BLOWERS,  ETC.  293 

Chimneys  must  he  made  with  air-tight  joints  to  prevent  leakage  of  air  on  account 
of  the  difference  of  pressure  inside  and  outside,  as  such  leakage  injures  the  draught. 
For  this  reason,  also,  the  use  of  telescopic  chimneys  is  very  objectionable,  causing  a 
marked  decrease  in  the  draught  of  the  boiler,  as  it  is  impossible  to  make  them  air-tight, 
there  being  necessarily  an  annular  space  of  more  or  less  width,  according  to  accuracy 
of  fitting,  between  the  standing  and  the  sliding  portions. 

Telescopic  chimneys  are  employed  only  on  board  of  war-steamers,  and  in  them  only 
because  a  considerable  portion  of  their  cruising  is  done  under  sail  alone.  The  position 
of  the  chimney  being  so  near  the  mainmast  as  to  prevent  the  setting  of  the  mainsail, 
the  inconvenience  is  sought  to  be  avoided  by  lowering  the  chimney  ;  the  height  of  the 
standing  portion,  however,  is  frequently  such  that,  even  when  reduced  to  the  minimum, 
the  mainsail  cannot  be  set.  The  principal  benefit  derived  from  telescoping  the  chimney 
is  to  make  the  vessel  look  more  like  a  sailing  ship— an  appearance  extravagantly  paid 
for  in  the  decreased  power  of  the  boiler  and  consequently  lessened  speed  of  the  vessel 
under  steam-power. 

If  it  was  desirable  to  keep  the  inner  surface  of  the  chimney  clean,  then  that  surface 
should  be  made  as  smooth  as  possible,  so  as  to  offer  the  least  resistance  to  the  ascending 
gaseous  currents,  which  would  be  particularly  important  in  the  case  of  small  chimneys 
and  rapid  currents.  But  it  is  found  advantageous  to  allow  the  inner  surface  to  remain 
coated  with  the  soot  and  tarry  hydrocarbons  deposited  from  the  gases  of  combustion, 
as  this  coating  efficiently  prevents  the  radiation  of  heat  from  the  outer  surface,  which 
it  is  desirable  to  avoid,  as  such  radiation  reduces  the  draught  by  lowering  the  tempera- 
ture of  the  gases  within  the  chimney.  So  long  as  it  is  the  surface  of  this  coating  which 
is  exposed  to  the  gaseous  currents,  the  smoothness  or  roughness  of  the  surface  to  which 
the  coating  adheres  is  of  but  little  importance.  Of  course  the  friction-resistance  of  the 
rough  surface  presented  by  the  hydrocarbon  coating  reduces  the  draught  more  than  a 
smooth  surface  of  metal,  and  to  that  extent  loses  what  it  gains  by  its  less  heat-conduct- 
ing power. 

To  regulate  the  draught  of  a  boiler,  and  consequently  its  rate  of  combustion,  a  valve, 
called  a  damper,  is  often  placed  within  the  flues,  which  slides  or  swings  across  their 
opening,  and  which  in  stationary  boilers  is  sometimes  regulated  automatically  by  the 
steam- pressure.  In  marine  boilers  the  damper  is  frequently  omitted  ;  when  used  it  is 
placed  within"  the  smoke-pipe,  near  its  lower  end,  and  consists  of  a  circular  plate  which 
swings  around  a  horizontal  spindle.  The  latter  projects  outside  the  pipe,  and  is  ope- 
rated by  hand  by  means  of  a  rope  or  chain  attached  to  a  wheel  or  crank  fixed  to  the 
spindle. 


294  STEAM  BOILERS.  CHAP.  XII. 

3.  Fixed  Chimneys. — Chimneys  are  built  up  of  separate  rings  or  courses ;  the 
length  of  the  courses  depends  on  the  size  of  the  plates  used  in  their  construction.  Plate- 
iron  varying  from  No.  6  to  No.  12  W.  G.  is  used  for  large  chimneys,  the  lower  courses 
being  made  of  heavier  iron  than  the  upper  courses.  The  upper  end  of  the  chimney 
is  stiffened  by  making  it  flaring,  or  by  riveting  a  heavy  wrought-iron  band  around  it  on 
the  outside.  The  longitudinal  as  well  as  the  transverse  seams  of  the  courses  are  some- 
times made  with  lap-joints  ;  the  lap  of  each  upper  course  must  be  placed  on  the  out- 
side, so  that  the  ascending  currents  of  gas  do  not  strike  against  the  ends  of  the  plates. 
A  better  and  neater  plan  is  to  use  butt-joints.  For  the  longitudinal  seams  the  butt- 
straps  may  be  placed  inside  the  pipe  ;  the  bands  which  connect  the  several  courses  at 
the  transverse  seams  are  placed  on  the  outside. 

When  the  chimney  is  bolted  rigidly  to  the  uptake  the  bolts  pass  in  some  cases 
through  the  flanges  of  angle-irons  riveted  around  the  top  of  the  uptake  and  around  the 
base  of  the  smoke-pipe,  or  a  stout  iron  band  is  riveted  around  the  upper  end  of  the  up- 
take, and  the  lower  end  of  the  pipe  fits  into  this  band  and  is  firmly  bolted  to  it.  With 
such  a  rigid  attachment  of  the  chimney  to  the  uptake  great  strains  are  often  thrown  on 
the  boiler  when  the  ship  rolls,  especially  when  the  stays  are  not  adjusted  with  great 
exactness.  On  this  account  it  is  better  not  to  attach  the  chimney  rigidly  to  the  boiler, 
but  to  let  it  simply  rest  on  the  uptake.  In  such  a  case  the  base  of  the  chimney  is 
reinforced  by  a  stout  iron  ring  riveted  to  it,  which  fits,  with  sufficient  clearance  to  allow 
for  expansion  and  irregularity  of  form,  in  an  annular  space  formed  on  the  top  of  the 
uptake  by  a  ring  of  angle-iron  riveted  around  the  mouth  of  the  uptake  ;  the  latter  pro- 
jects generally  a  few  inches  within  the  chimney. 

The  chimney  is  held  in  position  by  stays  attached  to  lugs  secured  to  the  bands 
which  connect  the  upper  courses,  and  leading  to  eye-bolts  placed  on  the  upper  deck  of 
the  vessel.  When  these  stays  are  formed  by  chains  they  are  attached  to  the  eye-bolts 
on  the  deck  by  short  lengths  of  rope  or  marline,  so  as  to  make  their  length  adjustable 
and  to  give  them  some  elasticity.  The  stays  are  sometimes  provided  with  turn-buckles, 
in  order  to  make  them  adjustable.  For  appearance'  sake  chimneys  are  often  made  to 
rake  aft,  but  such  an  arrangement  serves  no  practical  purpose. 

A  cylindrical  casing  surrounding  the  lower  part  of  the  chimney,  and  extending  from 
the  top  of  the  uptake  to  a  height  of  several  feet  above  the  upper  deck,  forms  an  annu- 
lar space,  generally  from  three  to  four  inches  wide,  around  the  pipe,  through  which  the 
air  can  circulate  freely,  intercepting  the  heat  radiated  from  the  chimney.  This  casing 
is  made  of  No.  10  or  No.  12  W.  G.  iron,  and  is  stiffened  at  the  top  by  a  heavier  wrought- 
iron  band.  It  is  secured  to  the  hatch-coaming  of  the  upper  deck.  In  some  cases  it 


SEC.  4.  UPTAKE,  CHIMNEY,  STEAM-JETS,  FAN-BLOWERS,  ETC.  295 

rests  on  the  top  of  the  boilers,  openings  being  cut  at  the  lower  end  for  the  circulation 
of  the  air.  The  top  of  this  jacket  projects  within  the  "  apron"  which  is  a  cover  riveted 
to  the  chimney  to  protect  the  annular  space  between  the  jacket  and  the  pipe  from  rain, 
etc.,  while  it  allows  the  free  escape  of  the  rising  air-currents.  For  the  further  protec- 
tion of  the  surrounding  wood- work  against  the  heat  of  the  chimney  an  annular  copper 
tank,  from  2£  to  3  inches  wide,  filled  with  water,  is  often  secured  around  the  air-casing 
within  the  hatch. 

The  following  directions  were  attached  to  the  drawing  of  a  chimney,  72  inches  in  dia- 
meter and  64  feet  high,  designed  for  the  U.  S.  S.  Algoma  and  class  in  1866 : 

"Each  pipe  to  be  made  of  seven  sections  vertically,  of  the  best  charcoal-iron.  The 
plates  of  the  three  lower  sections  to  be  made  of  No.  6  W.  G.  iron,  and  those  of  the  four 
top  sections  to  be  made  of  No.  8  W.  G.  iron.  The  vertical  seams  to  be  butted  with 
strips  of  iron  on  the  inside  ;  the  joints  to  be  made  very  close  ;  rivets  to  have  button- 
heads  on  the  outside.  The  horizontal  joints  to  be  made  with  neat  wrought-iron  bands 
on  the  outside.  The  bands  of  the  first  and  second  joints  from  the  top  to  have  each 
eight  lugs  for  stays.  Sixteen  stays  to  be  provided  for  each  pipe,  of  suitable  length,  in 
links  of  wrought-iron  \  inch  in  diameter,  with  proper  attachments  to  the  deck." 

4.  Hoisting-chimneys. — Hoisting  or  telescopic  chimneys  are  made  with  one  or 
two  movable  sections,  which  generally  slide  within  a  lower  fixed  section.  In  the 
'  Traite  elementaire  des  Appareils  a  Vapeur  de  Navigation,'  by  Ledieu,  an  illustration  is 
given  of  a  telescopic  chimney  of  oval  cross-section  with  the  hoisting  part  larger  than  the 
standing  part,  so  that  it  slides  outside  the  latter  within  the  air-casing.  This  arrange- 
ment seems  to  have  been  adopted  because  the  standing  part  of  the  pipe  is  divided  by  a 
partition  lengthwise  into  two  separate  passages.  In  another  example  given  in  the  same 
work,  where  the  standing  part  is  divided  in  a  similar  manner,  a  separate  semi-cylin- 
drical pipe  slides  within  each  division  of  the  fixed  pipe. 

The  usual  mode  of  constructing  telescopic  chimneys  for  United  States  naval  vessels 
is  illustrated  on  Plate  XVII. 

The  chimney  of  the  U.  S.  S.  Plymouth  (see  Plate  XVII.)  is  circular  in  cross-section 
and  has  one  movable  part.  The  fixed  pipe  has  an  inside  diameter  of  76£  inches  and  is 
made  of  No.  6  W.  G.  iron.  The  movable  pipe  has  an  inside  diameter  of  72  inches  and 
is  made  of  No.  8  W.  G.  iron.  The  plates  forming  each  course  are  butt-jointed,  being 
riveted  to  longitudinal  wrought-iron  bars,  -fa  inch  thick  and  3£  inches  wide,  placed 
inside  the  fixed  and  outside  the  movable  pipe  ;  the  heads  of  the  rivets  are  countersunk 
in  the  bars.  The  several  courses  are  connected  by  circumferential  butt-straps  placed 
outside  the  pipes.  The  top  of  the  fixed  pipe,  as  well  as  that  of  the  movable  pipe,  is 


296  STEAM  BOILERS.  CHAP.  XII. 

stiffened  by  an  iron  band,  4  inches  wide  and  about  %  inch  thick,  riveted  to  the  pipe  on 
the  outside.  To  each  of  these  bands  are  secured  six  wrought-iron  links  for  the  attach- 
ment of  stays.  A  wrought-iron  ring,  1J  inches  thick  and  2  inches  wide,  is  riveted 
around  the  top  of  the  fixed  pipe  on  the  inside.  Similar  rings  are  riveted  on  the  outside 
of  the  movable  pipe,  one  at  the  bottom  and  one  at  a  distance  of  34  inches  from  the  bot- 
tom. When  the  movable  pipe  is  lowered  it  rests  with  the  bottom  ring  on  the  top  of  the 
uptake  ;  when  it  is  hoisted  to  its  full  height  the  second  outside  ring  bears  against  the 
inner  ring  around  the  top  of  the  fixed  pipe,  forming  as  close  a  joint  as  practicable.  The 
longitudinal  bars  form  ways  for  guiding  the  pipe  when  it  is  being  raised  or  lowered. 
To  prevent  jamming  a  clearance  of  ^  inch  is  left  between  the  ways  and  the  If-inch 
rings  when  the  movable  pipe  is  concentric  with  the  fixed  pipe.  To  support  the  mova- 
ble section  when  hoisted  four  steel  bolts  are  tapped  through  composition  sleeves 
secured  at  a  suitable  height  to  the  fixed  pipe.  When  the  bolts  are  run  in  after  the 
pipe  is  hoisted  its  bottom  ring  rests  on  these  bolts. 

The  pipe  is  hoisted  by  four  wire  ropes,  f  inch  in  diameter,  leading  over  pulleys, 
7  inches  in  diameter,  secured  to  the  top  of  the  fixed  pipe.  One  end  of  each  wire  rope 
is  attached  to  a  lug  or  eye-bolt  fixed  to  the  bottom  ring  of  the  movable  pipe,  suit- 
able openings  being  cut  in  the  upper  part  of  the  fixed  pipe  and  in  the  lower  part  of 
the  movable  pipe  to  let  the  wire  ropes  pass  through.  The  other  end  of  each  rope 
leads  either  directly  or  over  guide-pulleys  to  a  windlass  carrying  four  drums  fixed  to 
one  horizontal  shaft.  This  windlass  is  mounted  over  the  hatch  of  the  lower  deck,  and 
is  operated  by  a  hand-crank  attached  to  an  endless  screw  which  gears  in  a  wheel  secured 
to  the  shaft  carrying  the  drums. 

Two  windlasses,  placed  on  opposite  sides  of  the  chimney,  may  be  used,  each  carry- 
ing two  drums.  These  two  windlasses  are  either  operated  independently  of  each  other 
or  they  are  connected  by  means  of  bevel-gearing  on  a  shaft  provided  with  hand-cranks. 
Steam-power  may  be  used  instead  of  hand -power  in  hoisting  the  pipe,  without  changing 
the  arrangement  of  the  drams  materially.  Sometimes  each  rope  leads  to  an  indepen- 
dent drum  operated  by  a  hand- crank  and  suitable  gearing  ;  but  in  this  case  it  is  found 
difficult  to  maintain  an  equal  tension  on  all  the  ropes  in  hoisting  the  pipe.  When 
several  drums  are  fixed  to  a  common  shaft  the  ropes  must  be  provided  with  an  arrange- 
ment for  adjusting  them  readily  to  the  proper  length  and  tension  ;  for  this  purpose  the 
shank  of  the  eye-bolt  to  which  each  rope  is  attached  passes  through  a  lug  fixed  to  the 
pipe,  and  is  secured  by  means  of  two  nuts,  one  placed  above  and  the  other  below 
the  lug. 

The  chimney  of  U.  S.  S.  Nipsic  has  two  movable  sections.     The  fixed  pipe  has  an 


SEC.  4.  UPTAKE,  CHIMNEY,  STEAM-JETS,  PAN-BLOWERS,  ETC.  297 

inside  diameter  of  79  inches  and  a  length  of  16  feet,  and  is  made  of  No.  7  W.  G.  iron. 
The  lower  movable  pipe  has  an  inside  diameter  of  74  inches  and  a  length  of  17  feet  3 
inches,  and  is  also  made  of  No.  7  W.  G.  iron.  The  upper  movable  pipe  has  an  inside 
diameter  of  69  inches  and  a  length  of  16  feet  10  inches,  and  is  made  of  No.  8  W.  G. 
iron.  All  seams  of  these  pipes  are  made  with  butt-joints  ;  the  longitudinal  butt-straps 
are  £  inch  thick  and  3£  inches  wide,  placed  inside  the  fixed  pipe  and  outside  the  two 
movable  pipes ;  the  heads  of  the  rivets  are  countersunk  in  the  straps.  Each  pipe  is 
stiffened  at  the  top  by  a  wrought-iron  band,  4  inches  wide  and  1  inch  thick,  placed  on 
the  outside  of  the  pipe.  The  bottom  end  of  each  pipe  has  on  the  outside  a  wrought- 
iron  band  2  inches  wide  and  from  1£  to  If  inches  thick.  A  similar  ring  is  placed 
around  the  top  of  the  fixed  pipe  and  of  the  lower  movable  pipe  on  the  inside.  When 
the  pipes  are  hoisted  to  their  full  height  the  rings  at  the  bottom  of  the  movable  sections 
bear  against  similar  rings  secured  inside  the  fixed  and  the  lower  movable  pipes,  26 
inches  from  the  top  of  the  pipes. 

The  upper  section  is  hoisted  simultaneously  with  the  lower  movable  section  by 
means  of  four  wire  ropes.  One  end  of  each  rope  is  secured  to  the  top  of  the  fixed  pipe. 
Passing  over  a  pulley  attached  near  the  top  of  the  lower  movable  section,  the  rope  leads 
down  between  the  upper  and  lower  movable  pipes,  and  has  its  other  end  attached  to  the 
band  at  the  bottom  of  the  upper  movable  pipe. 

The  hoisting-gear  of  the  lower  movable  pipe  is  of  a  novel  design.  A  chain,  made  of 
f -inch  iron,  has  both  ends  attached  to  a  wrought-iron  beam  fixed  across  the  lower  end 
of  the  movable  pipe,  and  passes  then  over  two  stationary  puUeys  secured  to  the  upper 
end  of  a  pipe  18  inches  in  diameter,  which  is  fixed  centrally  within  the  standing  part  of 
the  chimney  and  leads  down  through  the  uptake  into  the  fire-room.  The  bight  of  the 
chain  passes  around  a  movable  pulley  within  this  central  pipe.  This  pulley  carries  a 
swivel,  to  which  the  end  of  a  chain,  made  of  one-inch  iron,  is  attached,  that  leads  down 
through  the  central  pipe  to  a  drum  in  the  fire-room.  The  drum  is  revolved  by  hand- 
power  and  suitable  gearing. 

When  the  chimney  is  hoisted  it  has  a  height  of  44  feet  and  1  inch,  measured  from 
the  bottom  of  the  standing  pipe.  When  the  chimney  is  lowered  the  lower  movable  sec- 
tion rests  on  the  top  of  the  fixed  pipe,  and  the  upper  movable  section  rests  on  the  top  of 
the  lower  movable  section  ;  and  the  total  height  of  the  pipe,  measured  from  the  bottom 
of  the  fixed  pipe,  is  18  feet  f  inch. 

Double-hoist  chimneys  have  less  height  when  lowered  than  single-hoist  chimneys  ; 
this  is,  in  fact,  the  only  advantage  possessed  by  the  former  over  the  latter.  On  the  other 
hand,  all  the  disadvantages  connected  with  the  use  of  all  hoisting-pipes  are  greatly  in- 


298  STEAM  BOILERS.  CHAP.  XII. 

creased  in  the  case  of  the  former.  Compared  with  fixed  pipes  the  disadvantages  of 
hoisting-pipes  are  as  follows :  they  occupy  more  room  in  the  hatch  and  are  heavier ; 
their  first  cost  is  far  greater ;  they  are  more  liable  to  accidents,  and  much  labor  is  re- 
quired to  keep  their  gear  in  working  order ;  they  are  less  efficient  on  account  of  the 
sudden  changes  in  their  cross-sections  and  because  air-leaks  are  unavoidable  with  them. 

In  the  U.  S.  S.  Quinnebaug  and  class  the  chimney  is  made  with  one  movable  sec- 
tion, and  the  height  of  the  pipe  above  deck,  when  lowered,  is  reduced  by  letting  the 
movable  section  pass  through  an  opening  in  the  bottom  of  the  uptake  and  rest  on  the 
floor  of  the  fire-room.  When  the  pipe  is  hoisted  the  opening  in  the  uptake  is  closed  by 
a  door  secured  by  clamps.  The  lower  part  of  the  movable  pipe  has  two  large  openings 
opposite  to  each  other,  provided  with  doors,  in  order  to  form  a  passage  between  the  for- 
ward and  after  parts  of  the  fire-room  when  the  pipe  is  lowered. 

5.  Artificial  Draught :  Blast-pipe,  Steam-jets,  Fan-blowers. — To  attain  the 
best  possible  natural  draught  with  a  given  height  of  chimney  the  temperature  of  the 
column  of  hot  gas  within  the  chimney  has  to  be  so  great  that  from  25  to  33  per  cent,  of 
the  total  heat  generated  by  the  combustion  of  the  fuel  is  expended  in  producing  the 
draught.  (See  section  11,  chapter  ii.,  and  section  7,  chapter  iii.)  When  the  height  of 
the  chimney  and  the  bulk  and  weight  of  the  boiler  are  limited,  artificial  draught  has  to 
be  used  for  increasing  the  evaporative  power  of  the  boiler  beyond  a  certain  limit. 
Artificial  draught  has  the  great  advantages  that,  all  things  considered,  it  is  cheaper 
than  natural  draught  for  high  rates  of  combustion,  and  that  it  can  be  readily  adjusted 
for  the  combustion  of  different  kinds  of  fuel  and  for  widely  different  rates  of  combus- 
tion, so  that  a  given  boiler  may  be  worked  under  greatly  varying  conditions. 

The  general  measure  of  the  efficiency  of  the  mechanism  for  producing  artificial 
draught  is  the  ratio  of  the  power  expended  in  operating  the  mechanism  to  the  increase 
of  draught  produced  ;  the  increase  of  draught  may  be  measured  by  the  increase  in  the 
rate  of  combustion.  With  a  given  boiler  the  value  of  a  mechanism  for  producing  arti- 
ficial draught  depends  not  only  on  its  efficiency  as  measured  by  the  foregoing  rule,  but 
on  the  economic  evaporative  efficiency  of  the  boiler  with  different  rates  of  combustion ; 
on  the  weight  and  bulk  of  the  mechanism  ;  on  its  first  cost ;  and  on  the  labor  and  ex- 
pense of  operating  it  and  keeping  it  in  working  order. 

Artificial  draught  is  produced  either  by  diminishing  the  resistance  of  the  column  of  gas 
within  the  chimney  or  by  increasing  the  pressure  of  the  atmospheric  air  under  the  grate. 

To  produce  the  first  of  these  conditions  a  fan-blower  has  been  used  for  exhausting 
the  gases  escaping  up  the  chimney  ;  but  this  method  has  not  come  into  general  use  on 
account  of  practical  difficulties.  The  ordinary  method  is  to  use  a  jet  of  steam  in  the 


SEC.  5.  UPTAKE,  CHIMNEY,  STEAM-JETS,  FAN-BLOWERS,  ETC.  299 

chimney,  which  balances  by  its  impact  the  weight  of  the  column  of  gas  within  the 
chimney.  The  action  of  the  class  of  "fluid-on-fluid  impulse  machines"  to  which  the 
jet  belongs,  is  described  by  Rankine  in  the  following  words :  "A  stream  of  fluid,  mov- 
ing at  first  with  a  certain  velocity,  drives  and  carries  along  with  it  an  additional  stream, 
the  two  streams  finally  mingling  and  moving  together  with  a  velocity  less  than  that  of 
the  driving  stream." 

In  locomotives  the  blast  is  produced  by  discharging  the  exhaust  steam  from  the 
cylinders  into  the  chimney.  This  plan  can,  of  course,  be  used  only  with  high-pressure, 
non-condensing  engines,  and  is  applied  to  many  river-boats  and  to  tug-boats  and  simi- 
lar small  craft.  The  efficiency  of  such  a  blast  is  to  be  measured  by  the  increase  of  the 
evaporative  power  of  the  boiler  relatively  to  the  increase  of  back-pressure  produced  in 
the  steam-cylinders. 

"  The  effect  of  the  blast-pipe  in  producing  a  draught  depends  upon  its  own  diameter 
and  position,  on  the  diameter  of  the  chimney,  and  on  the  dimensions  of  the  fire-box, 
tubes,  and  smoke-box.  Mr.  D.  K.  Clark  has  investigated  the  influence  of  these  circum- 
stances from  his  own  experiments  and  from  those  of  Messrs.  Ramsbottom,  Polonceau, 
and  others,  and  has  shown  that  the  vacuum  in  the  smoke-box  is  about  0.7  of  the  blast- 
pressure  ;  that  the  vacuum  in  the  fire-box  is  from  £  to  \  of  that  in  the  smoke-box  ;  that 
the  rate  of  evaporation  varies  nearly  as  the  square  root  of  the  vacuum  in  the  smoke- 
box  ;  that  the  best  proportions  of  the  chimney  and  other  parts  are  those  which  enable 
a  given  draught  to  be  produced  with  the  greatest  diameter  of  the  blast-pipe,  because 
the  greater  that  diameter  the  less  is  the  back-pressure  produced  by  the  resistance  of  the 
orifice  ;  that  the  same  proportions' are  best  at  all  rates  of  expansion  and  at  all  speeds  ; 
and  that  the  following  proportions  are  about  the  best  known  : 

Sectional  area  of  tubes  within  ferrules    =  \  area  of  grate. 

Sectional  area  of  chimney  =  ^  area  of  grate. 

Area  of  blast-orifice  (which  should  be 
somewhat  below  the  throat  of  the 
chimney)  =  -fa  area  of  grate. 

Capacity  of  smoke-box  =  3  feet  X  area  of  grate. 

Length  of  chimney  =  four  times  its  diameter. 

"If  the  tubes  are  smaller  the  blast-orifice  must  be  made  smaller  also— for  exam- 
ple, if 

Sectional  area  of  tubes  within  ferrules     =  TV  area  of  grate, 

Then  area  of  blast-orifice  =  TV  area  of  grate." 

(Rankine,  '  Manual  of  the  Steam-engine:} 


300  STEAM  BOILERS.  CHAP.  XII 

When  condensing-engines  are  used  the  steam-jet  is  supplied  directly  from  the 
boiler.  Its  efficiency  is  to  be  measured  by  the  increase  of  evaporative  power  of  the 
boiler  relatively  to  the  weight  of  steam  expended  in  the  jet.  The  increase  of  draught 
produced  by  the  jet  depends  on  the  velocity  with  which  a  given  weight  of  steam  strikes 
against  the  column  of  gas  within  the  chimney,  and  on  the  area  of  that  column  immedi- 
ately acted  upon  by  the  jet.  C.  Wye  Williams  found  by  experiment  that  thirty  jets  of 
one-tenth  inch  sectional  area,  placed  three  inches  apart,  were  more  effective  than  sixty 
jets  of  one-quarter  inch  sectional  area  placed  one  inch  apart,  and,  moreover,  saved  an 
enormous  amount  of  steam. 

Isherwood  says  ('Experimental  Researches,'  vol.  ii.):  "It  is  found  experimentally 
that  with  a  properly-constructed  steam-jet,  composed  of  small  brass  nipples  or  hollow 
truncated  cones  inserted  in  concentric  rings  of  steam-pipe,  placed  in  the  smoke-pipe 
about  two  feet  above  its  bottom,  the  rings  being  so  spaced  as  to  equally  distribute  the 
area  of  the  smoke-pipe  over  them,  and  the  nipples  being  three  inches  between  centres 
on  the  rings,  the  expenditure  of  steam  of  40  Ibs.  per  square  inch  above  the  atmos- 
phere by  the  jet  to  raise  the  rate  of  combustion  in  the  water-tube  boiler  from  15$-  Ibs. 
per  square  foot  of  grate  per  hour  to  24  Ibs..,  the  air-supply  to  the  ashpit  being  copious 
and  not  brought  at  the  expense  of  the  draught,  is  7.22  per  centum  of  the  total  evapo- 
ration." 

The  jet  arrangement  designed  for  the  chimney  of  the  U.  S.  S.  Algoma  and  class 
(described  in  section  3  of  the  present  chapter)  consisted  of  three  rings  of  gas-pipe 
arranged  in  a  pyramidal  form  above  one  another,  with  a  vertical  distance  of  16  inches 
between  them,  and  connected  with  one  another  by  four  branch-pipes  screwed  into 
couplings.  These  rings  were  made  of  3-inch,  2^-inch,  and  2-inch  pipe,  and  had  an  out- 
side diameter  of  65  inches,  48|  inches,  and  32  inches  respectively,  the  larger  pipe  and 
ring  being  at  the  bottom  and  the  smaller  pipe  and  ring  at  the  top  of  the  system.  The 
steam-jets  issued  through  brass  nipples  screwed  into  the  rings  and  placed  3£  inches 
apart.  These  nipples  were  -ff  inch  long ;  the  opening  through  them  was  conical,  de- 
creasing from  ^  inch  near  the  bottom  to  ^  inch  near  the  top,  and  flared  at  the  bottom 
and  at  the  top  to  f  inch  and  J  inch  respectively. 

When  a  fan-blower  is  used  to  force  a  supply  of  air  directly  under  the  grates  the  ash- 
pit-doors and  furnace-doors  are  closed  tight,  and  the  mouths  of  the  ducts  which  convey 
the  air  from  the  blower  enter  the  ashpit  either  through  openings  at  the  back  of  the 
boiler  or  in  front  through  openings  in  the  ashpit-doors.  Each  branch-duct  is  provided 
with  a  valve  to  shut  off  the  air-supply  from  any  furnace  when  it  is  necessary  to  open 
the  ashpit  or  furnace  doors. 


SEC.  5.  UPTAKE,  CHIMNEY,  STEAM-JETS,  PAN-BLOWERS,  ETC.  301 

The  net  power  required  to  work  a  blower  may  be  calculated  by  means  of  the  formula 
given  in  section  12,  chapter  ii. 

"The  quantity  of  steam  required  to  work  the  fan-blower  rapidly  enough  to  produce 
a  combustion  of  even  35  Ibs.  of  anthracite  per  square  foot  of  grate-surface  per  hour  is 
quite  an  insignificant  per  centum  of  the  total  evaporation.  Such  an  apparatus  is  by  far 
the  most  economical  method  of  producing  the  draught ;  but  as  the  blast  must  be  de- 
livered beneath  the  grate-bars,  with  air-tight  ashpit-doors,  the  ventilation  of  the  fire- 
room  is  almost  wholly  destroyed  by  it,  and  the  firemen,  with  boilers  in  the  hold  of  ves- 
sels, find  the  heat  and  dust  insupportable.  The  fan-blower  is  generally  worked  by  a 
small  independent  steam-cylinder,  and  in  a  vessel  the  space  occupied  by  the  apparatus 
and  its  weight  are  considerable  ;  also,  the  trouble  of  looking  after  the  numerous  cocks, 
valves,  etc.,  connected  with  it,  and  the  unavoidable  complexity  attending  additional 
machinery,  have  operated  to  its  exclusion  on  board  of  marine  steamers."  (Isher- 
wood,  i  Experimental  Researches ^  vol.  ii.) 

Sometimes,  instead  of  forcing  the  air  directly  into  the  ashpits,  it  is  delivered  into 
the  fire-room,  which  is  enclosed  by  air-tight  bulkheads  and  decks,  and  has  no  outlet  for 
the  air  except  through  the  grates.  In  this  manner  an  increased  barometric  pressure  is 
produced  within  the  fire-room.  The  boilers  are  worked  with  open  ashpits,  and  the 
ventilation  of  the  fire-room  is  as  perfect  as  with  natural  draught.  When,  however,  the 
space  is  not  quite  air-tight  a  waste  of  power  ensues  ;  and  this  can  scarcely  be  avoided. 
This  plan  has  been  adopted  to  advantage  in  iron-clad  batteries,  torpedo-boats,  and 
similar  vessels,  which  have  to  be  constructed  with  tight  decks,  and  are,  consequently, 
dependent  upon  artificial  means  for  ventilation  and  a  supply  of  air  to  the  furnaces. 

In  some  instances  air  has  been  forced  through  nozzles  into  the  closed  ashpits  by 
means  of  steam- jets  ;  and  in  the  place  of  steam- jets  a  blast  of  air  supplied  by  a  fan- 
blower  has  been  tried  in  the  chimney. 

Koerting's  jet  apparatus  consists  of  a  series  of  short  nozzles 'gradually  increasing  in 
size  (see  figure  1,  Plate  XXX Y.)  According  to  the  inventor  the  number  and  dimen- 
sions of  these  nozzles  are  determined  by  the  following  considerations  :  1st,  to  make  the 
velocity  of  the  motive  fluid  a  maximum  as  it  escapes  under  a  varying  back-pressure  ; 
2d,  to  produce  an  intimate  mixture  of  the  propelling  fluid  with  the  fluid  to  be  set  in 
motion. 

The  tube  admitting  the  propelling  fluid  is  fixed  obliquely  at  the  side  of  the  smallest 
nozzle,  the  opening  of  which  can  be  varied  by  a  screw  in  order  to  regulate  the  admis- 
sion of  steam  or  compressed  air.  The  annular  openings  between  the  nozzles,  admitting 
the  air  to  the  propelling  jet,  gradually  increase  in  width  as  the  distance  from  the  open- 


302  STEAM  BOILERS.  CHAP.  XII. 

ing  admitting  the  steam  increases  and  the  velocity  of  the  jet  decreases.  Provision  is 
made  sometimes  to  vary  the  relative  position  of  the  conical  nozzles  by  means  of  a  screw, 
in  order  to  regulate  the  width  of  the  annular  spaces. 

In  the  first  nozzle  the  steam-jet  is  mixed  with  a  certain  quantity  of  air  and  forms 
with  it  a  new  jet,  which  becomes  mixed  in  the  successive  nozzles  with  additional  quan- 
tities of  air  entering  through  the  annular  spaces.  The  jet  gradually  decreases  in 
velocity,  while  the  volume  of  air  set  in  motion  increases  proportionately.  The  velocity 
attained  in  the  last  nozzle  corresponds  to  the  reqiiired  pressure. 

The  apparatus  represented  in  figure  1,  Plate  XXXV.,  is  designed  to  force  air  under 
the  grate  of  a  boiler  or  other  furnace.  With  an  initial  steam -pressure  of  40  Ibs.  per 
square  inch  the  pressure  of  air  produced  by  this  apparatus  is  equal  to  a  head  of  2 
inches  of  water. 

Apparatus  of  similar  construction  are  used  for  steam-jets  in  chimneys. 

6.  Experiments  with  Artificial  Draught  in  Marine  Boilers.— In  the  years 
1865-66  experiments  were  made  at  the  United  States  Navy- Yard,  New  York,  with 
various  devices  for  increasing  by  artificial  means  the  rate  of  combustion  in  marine 
boilers.  Steam  and  air  jets  of  various  forms  and  dimensions,  and  located  at  different 
heights  within  the  chimney,  were  tried,  and  air  was  forced  into  closed  ashpits  by  means 
of  fan-blowers  and  steam-jets  of  various  dimensions.  These  experiments  were  further 
varied  by  altering  the  dimensions  of  the  grates  and  the  ratios  of  calorimeter  and  heat- 
ing-surface to  grate-surface.  The  results  of  these  experiments  are  tabulated  in  the 
Report  of  the  Board  of  Engineers  convened  by  the  United  States  Navy  Department 
to  make  experiments  with  the  horizontal  fire-tube  boiler  and  the  vertical  water-tube 
boiler  of  the  Martin  type,  for  the  purpose  of  determining  the  relative  merits  of  these 
two  types  of  marine  boilers.  Since  the  primary  object  of  these  experiments  was  not  to 
determine  the  relative  efficiency  of  the  various  devices  used  for  producing  artificial 
draught,  the  results  of  all  the  experiments  are  not  comparable.  The  experiments  with 
the  vertical  water-tube  boiler  were  much  more  numerous  and  varied  than  those  with 
the  horizontal  fire-tube  boiler,  therefore  only  the  former  will  be  considered ;  and,  in 
order  to  eliminate  as  much  as  possible  all  uncertain  elements,  only  those  will  be 
selected  for  comparison  which  were  made  without  altering  the  heating-surface  and 
calorimeter  of  the  boiler,  and  in  which  the  grate  either  had  its  original  length  of  6 
feet  6  inches  or  was  shortened  to  6  feet  so  as  to  reduce  the  grate-surface  to  36  square 
feet. 

The  vertical  water-tube  boiler,  which  was  built  expressly  for  the  purpose  of  these 
experiments,  had  two  furnaces,  each  36  inches  wide  and  containing  a  grate  6  feet  6 


SEC.  6.  UPTAKE,  CHIMNEY,  STEAM-JETS,  FAN-BLOWERS,  ETC.  303 

inches  long.  It  had  a  separate  chimney  35  inches  in  diameter  and  60  feet  high  above 
the  grate,  and  it  contained  748  brass  tubes  of  2  inches  external  diameter  and  28f  inches 
long. 

Total  grate-surface 39  sq.  ft. 

Total  heating-surface 1264.81  sq.  ft. 

Ratio  of  grate  to  heating-surface 1  to  32.43 

Ratio  of  grate  to  calorimeter  of  tubes 7.04  to  1 

Ratio  of  grate  to  calorimeter  of  chimney 5.79  to  1 

Each  experiment  lasted  from  48  to  80  hours  continuously.  In  the  experimental 
boiler  the  evaporation  took  place  under  atmospheric  pressure.  The  steam  for  operating 
the  jet  or  fan  was  supplied  by  an  independent  boiler,  in  which  the  pressure  ranged 
from  25  to  40  Ibs.  per  square  inch  above  the  atmosphere.  The  water  supplied  to  both 
these  boilers  .was  measured  in  separate  tanks.  The  coal  was  Pennsylvania  anthracite 
of  "egg-size,"  free  from  dust,  and  the  amount  used  was  accurately  weighed. 

The  quantities  given  in  columns  b,  c,  d,  e  of  the  following  table  are  taken  directly 
from  the  tables  accompanying  the  above-mentioned  report,  except  when  they  represent 
the  mean  results  of  several  experiments,  which  are  calculated  from  the  quantities  given 
in  the  original  tables.  The  quantities  contained  in  columns  /,  /„  g,  g,,  h,  Tit,  j, ./.  are 
calculated  from  the  results  recorded  in  the  original  tables. 

Column  f  shows  the  quantity  of  steam  expended  for  blast  in  per  centum  of  the 
total  weight  of  water  evaporated,  and  column  fl  the  weight  of  water  of  212°  Fahr. 
evaporated  under  atmospheric  pressure  equivalent  to  the  actual  weight  of  steam  ex- 
pended for  blast  per  hour. 

Columns  g,  ga  show  the  quantity  of  steam,  in  pounds,  available  for  useful  work,  or 
the  difference  of  the  weight  of  steam  expended  for  blast  and  of  the  total  weight  of 
water  evaporated. 

Columns  h,  Ji0  and  /,  j,  show  the  cost  of  producing  the  increase  in  the  rate  of  com- 
bustion and  in  the  evaporative  power  of  the  boiler  in  each  experiment,  expressed  in 
pounds  of  steam  expended  in  blast  for  each  additional  poutid  of  coal  burned  and  of 
water  evaporated  respectively. 

On  account  of  the  unavoidable  differences  in  the  quality  of  the  coal,  and  on  account 
of  the  influence  of  the  variations  in  the  rates  of  combustion  on  the  economic  evapora- 
tive efficiency  of  the  boiler,  the  tabulated  results  indicate  only  approximately  the  rela- 
tive value  of  the  various  methods  tried. 

Comparing  the  results  of  experiments  Nos.  3,  4,  5,  6,  and  7,  it  will  be  seen  from 


304:  STEAM  BOILERS.  CHAP.  XH 

columns  h,  7ia  that  when  the  jet-coil  is  supplied  with  nozzles  of  proper  form  and  dimen- 
sions the  efficiency  of  the  steam-jet  is  nearly  twice  as  great  as  when  the  steam  issues 
through  plain  holes  drilled  in  the  coil.  Columns  h,  7i0  indicate  likewise  that  in  ex- 
periments Nos.  4,  6,  6,  and  7  the  weight  of  steam  expended  for  each  additional  pound 
of  coal  consumed  did  not  vary  greatly. 

Comparing  experiments  Nos.  8,  9,  10N 11,  12,  and  13  with  the  preceding  ones,  it  ap- 
pears that  the  large  single  nozzle  produced  on  the  whole  a  better  useful  effect  than  the 
steam-jet  consisting  of  numerous  small  nozzles.  This  result,  which  apparently  contra- 
dicts other  experiments,  may  be  explained  by  the  fact  that  the  chimney  was  not  of 
large  diameter,  and  that  the  coils  of  the  jet-pipe  formed  a  serious  obstruction  to  the 
passage  of  the  gases  in  the  smoke-pipe.  To  preserve  the  proper  calorimeter  the  smoke- 
pipe  was  enlarged  to  a  diameter  of  38  inches  at  the  place  where  the  jet-coil  was  situ- 
ated ;  a  better  result  would  probably  have  been  obtained  by  giving  to  the  coil  the 
pyramidal  form  described  in  section  5  of  this  chapter,  since  it  obstructs  less  the  cross- 
section  of  the  pipe. 

The  height  of  the  single  jets  above  the  grate  was  varied  in  several  experiments  with- 
out producing  any  marked  difference  in  the  results.  When,  however,  the  jet  was 
placed  only  6  feet  below  the  top  of  the' chimney  it  became  ineffective.  A  single  steam- 
jet  placed  in  each  back -connection  showed  likewise  no  useful  results. 

The  great  efficiency  of  the  fan-blower  in  increasing  the  rate  of  combustion  by  forc- 
ing air  into  closed  ashpits  is  illustrated  in  columns  h,  ~hm  experiments  Nos.  16,  17,  and 
18 ;  and  columns  j,  j\  show  how  far  the  relative  economy  of  this  system  of  forcing  the 
draught  is  maintained  for  high  rates  of  combustion  with  decreased  economic  evapora- 
tive efficiency  of  the  boiler.  In  experiment  No.  18  the  economic  evaporation  falls  so 
low  that  the  boiler  actually  furnishes  less  available  steam  than  in  experiment  No.  17, 
although  the  rate  of  combustion  is  nearly  33  per  cent,  greater  in  the  former  case  than  in 
the  latter.  This  great  falling-off  in  economic  evaporation  is  probably  to  some  extent 
owing  to  the  fact  that  too  large  an  amount  of  air  entered  the  furnaces  relatively  to  the 
weight  of  fuel  consumed,  and  a  better  result  might  have  been  obtained  if  a  thicker  bed 
of  fuel  could  have  been  maintained  or  if  coal  of  smaller  size  had  been  used.  With 
smaller  coal  the  interstices  affording  passage  to  the  entering  air  are  more  numerous, 
narrower,  and  more  tortuous,  and  a  larger  amount  of  surface  of  the  incandescent  fuel  is 
presented  to  the  air.  A  great  increase  in  efficiency  has  resulted  in  some  cases  from  the 
use  of  smaller  coal  with  forced  draught. 


SEC.  6. 


UPTAKE,  CHIMNEY,  STEAM-JETS,  FAN-BLOWERS,  ETC. 


305 


w 

H 


tn 

W 

a 

w 
Q 

</) 

D 

o 


x 

h 


1O 

vo 
oo 


•ON 


a  s? 


o 
« 


S1      «& 


pu   re^« 
>>EJ    i «  s  ~ 


JO   -q 
JOj 


dsn  joj 

U1C31S 


JO   spunoj 


3JKJ 


D  jo 

aqj 
' 


•bsjadpatunsuoo 
IBOO    jo   -q|  jad 

*-S3Jd  -SOUI1B  J3p 

-un  -j  oZie  tuojj 

p.dEA3    J3JE.VI    JO 

•        in  «ise|q  Joj 


jo  i  pspusdxi  AIII  i  is 
-uenb  ssaj  'jno'u 

jad          P3JBJ3U33  ,_ 

meais  jo  spunoj  o  «-" 


Iff; 


11  j       i 


:         '3. 


i  i  i     i 

iR  >o 


il    i 


\*        *      f=        = 

rf;         «o-      o-  • 


"jnoij  J3<1  jffBjq 
JOj  papuadxa 
meals  jo  spunoj 


CHAPTER  XIII. 

STEAM-ROOM   AND   SUPERHEATERS. 

1.  Capacity  of  Steam-room. — Too  large  a  steam-room  not  only  increases  the 
bulk  and  weight  of  the  boiler  unnecessarily,  but  increases  its  heat-radiating  surface. 
It  is  useless  to  increase  the  steam-space  beyond  a  certain  limit  for  the  purpose  of  stor- 
ing up  steam  to  meet  any  sudden  demand  arising  from  irregular  loads  on  the  engines  ; 
for  a  simple  calculation  will  show  that  the  heated  water  contained  in  the  boiler  can  be 
relied  upon  for  a  far  greater  supply  of  steam  in  case  of  a  sudden  emergency  than  could 
be  obtained  by  any  admissible  increase  in  the  capacity  of  the  steam-room. 

When  the  capacity  of  the  steam-room  is  small  relatively  to  the  quantity  of  steam 
drawn  from  the  boiler  per  stroke  of  engine,  the  pressure  in  the  boiler  fluctuates  greatly. 
Any  sudden  fall  of  pressure  causes  a  violent  ebullition  of  the  water  heated  to  the  boil- 
ing-point, producing  injurious  pulsations  and  priming.  To  diminish  the  fluctuations  of 
pressure  in  the  boiler  the  latter  must  carry  a  large  amount  of  water  relatively  to  the 
amount  evaporated  in  a  unit  of  time,  and  the  capacity  of  the  steam-room  must  be  pro- 
portioned to  the  capacity  of  the  cylinders.  With  engines  working  with  a  high  rate  of 
expansion,  and  making  relatively  few  revolutions  per  minute,  the  capacity  of  the  steam- 
room  has  to  be  relatively  greater. 

Authorities  differ  as  to  the  best  proportions  of  steam-room  and  water-room  in  boilers. 
According  to  Bourne  ('Handbook  of  the  Steam-engine'),  the  total  capacity  or  bulk  of 
a  marine  boiler,  exclusive  of  chimney,  is  usually  about  8  cubic  feet  for  each  cubic  foot 
of  water  evaporated  per  hour,  divided  in  the  proportion  of  6.5  cubic  feet  devoted  to  the 
water,  furnaces,  and  tubes,  and  1.5  cubic  feet  occupied  as  steam-room.  The  capacity  of 
the  steam-room  of  several  boilers  illustrated  in  this  book  will  be  found  in  Table  XXII., 
chapter  vii. 

In  the  French  navy  experience  has  developed  the  fact  that,  with  rectangular  boilers 
of  ordinary  dimensions  of  the  type  illustrated  in  figure  106  and  on  Plate  XVII.,  and 
burning  about  20  Ibs.  of  coal  per  square  foot  of  grate  as  a  maximum,  when  the  capacity 
of  the  steam-room  is  equal  to  the  volume  of  steam  consumed  by  the  engines  during  14 

306 


SEC.  2.  STEAM-ROOM  AND  SUPERHEATERS.  307 

seconds,  no  water  is  carried  over  into  the  cylinders ;  bnt  when  it  contains  steam  for 
only  12  seconds  the  steam  is  generally  very  wet.  With  cylindrical  boilers  working 
with  high  pressures,  and  having  a  capacity  of  steam-room  equal  to  the  volume  of  steam 
consumed  by  the  engines  during  16  seconds,  water  is  carried  over  at  times  ;  while  simi- 
lar boilers  containing  steam  for  20  seconds  give  no  such  trouble. 

When  the  steam-room  is  contained  partly  in  a  steam-drum  to  which  the  steam -pipe 
leading  to  the  engines  is  connected,  the  opening  by  which  the  drum  communicates  with 
the  steam-space  within  the  shell  of  the  boiler  must  be  arranged  in  such  a  manner  that 
the  steam  has  no  tendency  to  enter  with  a  violent  rush,  lifting  the  water  or  carrying  it 
along  in  the  form  of  spray.  Height  of  steam-space  is  important  especially  in  marine 
boilers,  in  which  the  water  is  frequently  greatly  agitated  in  consequence  of  the  motion 
of  the  vessel. 

Height  of  steam-room  is  also  necessary  in  order  to  afford  vertical  space  for  the  sepa- 
ration from  the  steam  of  the  water  carried  up  with  it  mechanically.  This  separation 
is  effected  by  the  greater  gravity  of  the  water  enabling  it  to  fall  back  after  being 
carried  to  a  certain  height,  so  that  a  definite  height  is  absolutely  necessary  for  the 
operation.  No  amount  of  steam-room  a  few  inches  high  will  enable  a  boiler  to  fur- 
nish dry  steam,  while  with  a  considerable  height  a  comparatively  small  volume  of  steam- 
room  will  be  efficient. 

The  greater  value  of  steam-drums  upon  a  boiler  than  their  volume  of  steam-room 
within  the  shell  is  due  to  the  simple  fact  of  their  greater  height.  The  real  purpose  of 
the  drum  is  not  so  much  to  gain  increased  steam-room  as  increased  height  of  steam- 
room.  And  the  wonderful  efficiency  of  steam-chimneys,  as  they  are  called — that  is,  an- 
nular steam-drums  enveloping  concentrically  the  base  of  the  chimney — arises  not  only 
from  the  superheating  which  the  steam  obtains  in  them,  but  from  the  very  considerable 
height  given  to  them,  whereby  the  water  entrained  by  the  steam  has  time  and  space  to 
become  separated  very  thoroughly  by  its  greater  gravity. 

2.  Steam-drums. — In  rectangular  boilers  of  naval  vessels  the  steam-space  is  gene- 
rally contained  entirely  within  the  shell,  although  sometimes  a  low  steam-drum,  sur- 
rounding the  uptake,  is  added.  Cylindrical  and  semi-cylindrical  boilers  are  nearly 
always  provided  with  steam-drums,  which  generally  form  an  annular  space  around 
the  base  of  the  chimney ;  with  this  arrangement  the  steam-drums  occupy  the  most 
convenient  place  in  the  boiler-hatch,  and  a  considerable  amount  of  superheating- 
surface  is  gained.  These  drums  are  either  built  directly  on  the  top  of  the  boiler,  their 
bottom  being  open  to  the  steam-space,  or  they  are  separate. structures  which  are  con- 
nected by  pipes,  provided  with  stop-valves,  with  the  steam-space  within  the  shell  of  the 


308  STEAM  BOILEES.  CHAP.  XIII. 

boiler.  In  merchant-vessels  the  steam-drums  are  generally  placed  vertically  on  the  top 
of  the  boilers,  in  order  to  gain  additional  height  of  steam-space.  In  war-vessels  they 
lie  horizontally  in  the  upper  spandrels  formed  by  the  cylindrical  shells  of  each  pair  of 
adjacent  boilers,  and  are  greatly  less  efficient.  All  steam-drums  should  be  provided 
with  manholes,  and  should  be  made  roomy  enough  to  be  accessible  for  examination  and 
cleaning.  They  should  be  provided  with  drain-pipes  for  drawing  off  any  water  which 
may  have  been  carried  into  them  by  priming  or  formed  within  them  by  the  condensation 
of  the  steam. 

When  a  steam-drum  or  dome  is  built  vertically  on  the  cylindrical  shell  of  a  boiler 
it  is  the  usual  practice  to  cut  a  hole,  corresponding  in  diameter  to  the  drum,  in  the  shell 
of  the  boiler,  and  secure  the  cylindrical  drum  to  the  shell  by  means  of  an  angle-iron 
ring.  When  the  drum  is  not  of  large  diameter,  as  in  locomotive  boilers,  the  top  is 
often  made  hemispherical  to  avoid  the  use  of  stays.  It  is  evident  that  the  cylindrical 
shell  is  very  much  weakened  by  the  large  hole,  unless  a  heavy  wrought-iron  strengthen- 
ing-ring is  riveted  around  the  opening.  Sometimes,  instead  of  cutting  a  large  opening 
in  the  shell,  a  great  number  of  small  holes  are  drilled  in  the  shell  to  establish  communi- 
cation between  the  steam-space  within  the  boiler  and  the  interior  of  the  dram.  The 
perforated  plate  is  intended  to  check  a  rush  of  water  into  the  drum  and  to  cause  less 
reduction  of  strength  of  the  boiler-shell.  The  only  addition  given  by  it  to  the  strength 
of  the  shell  is  what  is  due  to  the  stiffne&s  of  the  curved  plate.  In  other  cases  the  shell 
is  cut  away  only  sufficiently  to  allow  a  man  to  pass  from  the  boiler  into  the  dome,  the 
opening  being  made,  however,  so  large  that  the  rush  of  steam  through  it  does  not  induce 
priming. 

In  these  cases  the  portion  of  the  shell  which  forms  the  bottom  of  the  drum  is  not 
subjected  to  direct  tension,  like  the  rest  of  the  shell,  by  the  pressure  of  steam.  Conse- 
quently the  tangential  forces  due  to  the  tension  on  the  shell  tend  to  straighten  this  por- 
tion of  the  shell,  and  to  open  out  the  lower  part  of  the  cylindrical  shell  of  the  drum, 
and  thus  throw  a  strain  on  the  flange  of  the  drum  at  the  opposite  sides.  To  pre- 
vent this  strain  the  bottom  of  the  drum  must  be  subjected  to  a  tension  equal  to  that 
on  the  rest  of  the  shell,  which  may  be  effected  to  a  certain  extent  by  making  the  top  of 
the  drum  flat  and  tying  it  by  vertical  rods  to  the  cylindrical  boiler-shell  forming  the 
bottom  of  the  drum. 

Straight  braces  may  also  be  placed  across  the  opening  of  the  drum  transversely  to 
the  shell,  thus  restoring,  in  a  measure,  the  strength  due  to  the  portion  of  the  shell  cut 
out  for  the  drum. 

In  small  cylindrical  boilers  the  vertical  steam-domes  are  sometimes  made  with  a 


SEC.  3.  STEAM-ROOM  AND  SUPERHEATERS.  309 

spherical  top  and  with  a  contracted  neck  at  the  bottom.  This  neck  is  made  of  stont 
material  and  with  a  broad  flange,  which  serves  to  compensate  in  a  great  measure  for  the 
loss  of  strength  due  to  cutting  a  hole  in  the  shell  of  the  boiler. 

3.  Superheaters. — The  general  principles  according  to  which  the  theoretical  and 
the  practical  efficiency  of  superheaters  are  to  be  determined  have  been  stated  in  sections 
9  and  10,  chapter  iii. 

In  nearly  all  marine  boilers  a  portion  of  the  uptake  passes  through  the  steam-space, 
and,  in  a  measure,  dries  or  superheats  the  steam.  In  all  sectional  water-tube  boilers 
the  tubes  forming  the  steam-space  act  as  efficient  superheaters,  and  in  launch  boilers 
the  steam  passes  frequently  through  a  coiled  pipe  in  the  uptake  before  it  is  led  off  to 
the  engine.  In  the  vertical  fire-tube  boiler  the  water-level  is  carried  some  distance 
below  the  upper  tube-sheet,  and  the  upper  ends  of  the  tubes  and  the  uptake  form 
superheating-surfaces.  In  the  vertical  water-tube  boiler  of  the  Martin  type,  likewise, 
the  water  may  be  earned  with  safety  several  inches  below  the  upper  tube-sheet,  and 
efficient  superheating-surface  will  thus  be  gained.  The  vertical  steam-drums  of  marine 
boilers  are  commonly  traversed  by  one  or  several  large  flues  for  the  purpose  of  drying 
or  superheating  the  steam.  In  some  cases  the  steam-drum  surrounding  the  base  of  the 
chimney  is  divided  by  partitions  into  several  compartments,  which  communicate  with 
one  another  by  openings  at  opposite  ends  in  such  a  manner  that  the  steam  has  to  pass 
in  succession  through  all  the  different  compartments  before  it  enters  the  steam-pipe, 
and  thus  is  forced  to  remain  a  longer  time  in  contact  with  the  superheating-sur- 
face. 

In  the  high-pressure  cylindrical  boilers  of  United  States  naval  vessels  superheating- 
surface  is  provided  by  letting  the  steam-pipe  pass  several  times  through  the  whole 
length  of  the  uptakes  along  the  fronts  of  the  boilers. 

By  means  of  flues  traversing  or  surrounding  the  steam-drum  or  the  upper  part  of 
the  boiler  the  steam  may  be  effectually  dried  and  its  temperature  may  be  raised  to  a 
point  exceeding  somewhat,  but  not  very  much,  the  boiling-point  corresponding  to  the 
pressure  in  the  boiler.  When  a  much  higher  temperature  is  to  be  given  to  the  steam 
the  superheating  has  to  be  effected  in  a  separate  chamber  containing  a  larger  amount  of 
heating-surface  than  can  be  obtained  conveniently  by  the  above-mentioned  arrange- 
ments. 

The  superheater  of  TJ.  S.  S.  Plymouth  (see  Plate  XYII.)  consists  of  a  box  extending 
along  the  front  of  the  boiler  and  traversed  by  numerous  vertical  brass  tubes,  through 
which  the  products  of  combustion  pass  from  the  front-connections  to  the  uptake.  At 
one  end  of  the  box  the  saturated  steam  is  admitted  from  the  boiler  through  suitable 


310  STEAM  BOILERS.  CHAP.  XIII. 

pipes  and  stop- valves,  and  at  the  other  end  the  superheated  steam  is  carried  off  to  the 
main  steam-pipe. 

In  other  superheaters  horizontal  pipes  are  used,  and  these  are  often  arranged  in  two 
groups  connected  at  the  ends  by  chambers  in  such  a  manner  that  the  steam  passes 
twice  through  the  whole  length  of  the  superheater,  entering  through  one  group  and  re- 
turning through  the  other,  before  it  is  discharged  into  the  steam-pipe. 

Superheaters  constructed  of  flat  plates,  after  the  plan  of  Lamb  and  Sumner's  boiler 
(see  section  1,  chapter  xi.),  have  been  much  used  in  England.  Many  other  devices 
have  been  tried  with  the  view  of  gaining  a  large  amount  of  efficient  heating-surface  in  a 
cheaply- constructed  apparatus. 

The  superheaters  are  generally  arranged  in  the  uptake  of  the  boiler,  so  as  to  utilize 
some  of  the  heat  of  the  escaping  gases.  It  is  evident  that  when  a  high  degree  of  super- 
heating is  desired  considerable  difference  must  exist  between  the  temperatures  of  the 
gases  in  the  uptake  and  of  the  saturated  steam  in  the  boiler ;  and  to  obtain  this  dif- 
ference the  water-heating  surface  of  the  boiler  must  be  made  small  relatively  to  the 
amount  of  coal  burnt  in  a  unit  of  time.  Besides,  the  additional  resistance  offered  by  the 
superheating  apparatus  to  the  escaping  gases  makes  it  necessary  that  the  chimney  tem- 
perature should  be  correspondingly  increased,  in  order  to  maintain  the  same,  rate  of 
combustion  as  without  the  superheating  apparatus. 

A  great  increase  of  efficiency  has  been  obtained  in  cases  where  such  superheaters 
have  been  added  to  boilers  already  built  which  were  subject  to  priming  or,  being  defi- 
cient in  heating-surface,  discharged  the  gases  at  a  higher  temperature  than  was  required 
for  the  desired  rate  of  combustion.  The  saving  in  fuel  expended  for  a  given  amount  of 
work,  effected  by  the  introduction  of  superheating  apparatus,  has  amounted,  in  a  num- 
ber of  cases  cited  by  Bourne  ('A  Treatise  on  the  Steam-engine'),  to  from  18  to  34  per 
centum. 

Superheaters  of  the  foregoing  description,  with  their  steam-pipe  connections  and 
stop-valves,  add  largely  to  the  weight  and  cost  of  boilers ;  and  unless  they  are  easily 
accessible  for  sweeping  (which  is  frequently  not  the  case),  the  efficiency  of  their  heating- 
surface  is  soon  impaired  and  the  draught  of  the  boiler  is  often  seriously  affected  by  the 
accumulation  of  soot.  The  most  serious  troubles,  however  (which  have  brought  super- 
heaters somewhat  into  disrepute),  are  due  to  the  rapid  corrosion  of  the  iron  of  which 
superheaters  are  constructed,  and  to  the  leakage  of  their  tubes.  The  rapid  corrosion  of 
superheating-surfaces  has  been  observed  for  a  long  time,  even  in  the  case  where  the  de- 
gree of  superheating  was  relatively  small,  as  in  steam-drums  traversed  by  flues,  but  its 
causes  have  not  been  definitely  determined.  The  leakage  of  the  tubes  after  short  use  is 


SEC.  3.  STEAM-ROOM  AND  SUPEKHEATEBS.  ,  311 

probably  mainly  owing  to  the  fact  that,  after  the  fires  are  lighted,  some  time  elapses 
before  steam  is  formed  in  the  boiler,  and  the  hot  gases  passing  through  the  empty 
superheater  raise  the  metal  to  an  unduly  high  temperature.  To  remedy  this  defect  it  is 
proposed  to  keep  the  superheater  filled  with  water  until  steam  is  formed  in  the  boiler. 

Some  years  ago  many  United  States  naval  vessels  were  furnished  with  special  super- 
heating-boilers,  one  being  provided  for  each  pair  of  main  boilers  containing  in  all  four- 
teen furnaces.  Each  superheating-boiler  contained  one  furnace  of  the  usual  dimen- 
sions. The  products  of  combustion,  after  passing  through  return-flues,  situated  over 
the  furnace,  to  a  front-connection,  passed  through  a  set  of  horizontal  iron  tubes  to  an 
upper  back-connection,  and  returned  thence  through  another  set  of  like  tubes  to  an 
upper  front-connection,  which  communicated  with  the  uptake  of  the  main  boilers.  The 
lower  flues  of  the  boiler  were  kept  covered  with  water,  and  the  double-return  tubes  fur- 
nished the  superheating-surface.  The  superheating-boiler  communicated  with  the 
main  steam-pipes  through  stop- valves,  arranged  in  such  a  manner  that  the  steam  from 
the  main  boilers  would  either  pass  wholly  or  in  part  through  the  superheaters,  or  go 
directly  to  the  engines.  These  boilers  were  efficient  superheaters ;  but  they  were 
rapidly  destroyed  by  corrosion,  because  their  interior  was  inaccessible  and  the  iron 
superheating-tubes  were  left  without  the  coating  of  scale  which  protects  the  iron  water- 
heating  tubes  of  marine  boilers  effectually.  In  the  TJ.  S.  S.  Congress  each  of  these 
superheating-boilers  was  3  feet  10  inches  wide,  10  feet  3  inches  long,  and  9  feet  9  inches 
high,  and  its  weight  complete  was  19,000  Ibs.  The  superheating  effected  was  about  30° 
Fahr.  above  the  saturation  temperature. 

Independent  superheating-boilers  possess  the  advantage  that  any  degree  of  super- 
heating may  be  obtained  in  them  with  great  exactness  by  regulating  the  rate  of  com- 
bustion in  the  furnace  ;  furthermore,  the  efficiency  of  the  main  boilers  is  entirely  inde- 
pendent of  the  efficiency  of  the  superheaters  ;  any  derangement  of  the  latter  does  not 
affect  the  former.  The  additional  space  occupied  by  them  is  an  important  element  in 
determining  their  relative  usefulness  ;  but  in  naval  vessels  it  may  often  be  advisable  to 
sacrifice  room  on  the  floor  of  the  vessel  in  order  to  get  a  lower  and  a  more  reliable 
boiler. 

The  superheating  arrangement  of  the  U.  S.  S.  Eutaw  (built  in  1863)  consisted  of  two 
groups  of  horizontal  tubes,  with  the  ends  secured  in  tube-plates.  Each  group  con- 
tained 176  iron  tubes  1|  inches  in  diameter  and  21  inches  long  between  the  tube-plates. 
At  one  end  the  two  groups  communicated  by  means  of  a  common  chamber  formed  by 
an  iron  casting  bolted  to  the  tube-plate,  and  at  the  other  end  each  group  had  a  separate 
connection  formed  by  an  iron  casting  provided  with  a  nozzle  and  likewise  bolted  to  the 


312  STEAM  BOILERS.  CHAP.  XIII. 

tube-plate.  This  superheater  was  placed  in  the  tube-box  of  one  of  the  wing  furnaces 
of  each  boiler,  from  which  the  vertical  water-tubes  had  been  removed  with  the  excep- 
tion of  six  rows  at  the  back  of  the  box,  left  for  the  purpose  of  reducing  somewhat  the 
temperature  of  the  gases  before  they  impinged  on  the  superheating-tubes.  The  tubes 
of  the  superheater  were  placed  across  the  tube-box,  and  the  nozzles  of  the  connections 
projected  through  openings  in  the  side  of  the  boiler.  To  the  nozzle  nearest  the  front 
of  the  boiler  a  pipe  bringing  the  saturated  steam  to  the  superheater  was  bolted,  and  to 
the  other  nozzle  another  pipe  was  bolted  carrying  the  superheated  steam  to  the  main 
steam-pipe.  These  pipes  were'  all  controlled  by  stop-valves,  so  that  the  superheater 
could  be  shut  off  when  the  fire  was  hauled  from  the  furnace,  and  the  engine  could  be 
supplied  with  saturated  steam,  or  superheated  steam,  or  a  mixture  of  saturated  and 
superheated  steam. 

Each  of  the  two  boilers  contained  five  furnaces,  and  the  two  boilers  contained  in  the 
aggregate  200  square  feet  of  grate-surface,  4,536  square  feet  of  water-heating  surface, 
and  1,058  square  feet  of  superheating-surface. 

Using  natural  draught  and  burning  11.67  Ibs.  of  anthracite  coal  per  square  foot  of 
grate  per  hour,  the  temperature  of  the  steam  was  raised  from  270.2°  Fahr.  when  satu- 
rated to  365.0°  Fahr.  when  superheated. 

Using  a  fan-blower  and  burning  27  Ibs.  of  anthracite  coal  per  square  foot  of  grate  per 
hour,  the  temperature  of  the  steam  was  raised  from  295.0°  Fahr.  when  saturated  to 
380.0°  Fahr.  when  superheated. 

One  of  the  greatest  practical  objections  to  the  use  of  separate  tubular  superheaters 
as  described  is  the  impossibility  of  cleaning  the  steam  side  of  the  surfaces.  The  inte- 
rior of  the  tubes  or  the  spaces  between  the  tubes,  as  the  construction  may  be,  become 
filled  with  the  mud  and  grease  carried  over  from  the  boiler  by  priming  or  foaming,  and 
there  is  no  means  of  removing  these  substances  without  destroying  the  superheater. 


CHAPTEK  XIV. 

SETTING  AND   ERECTION  OF  BOILERS. 

1.  Setting  of  Boilers. — The  weight  of  large  boilers  must  be  well  distributed  over 
the  floor  of  the  vessel.  When  the  boilers  are  placed  so  that  the  fire-room  runs  in  the 
fore-and-aft  direction  of  the  vessel  they  rest  generally  on  two  keelsons.  To  protect  the 
bottom  of  the  boilers  from  the  bilge- water  a  tight  platform  is  often  built  on  the  keel- 
sons for  the  boilers  to  rest  on. 

The  following  directions  are  given  by  Bourne  for  setting  flat-bottomed  boilers  in 
wooden  vessels  :  "In  the  setting  of  marine  boilers  care  must  be  taken  that  no  copper 
bolts  or  nails  project  above  the  wooden  platform  upon  which  they  rest,  and  also  that 
no  projecting  copper  bolts  in  the  sides  of  the  ship  touch  the  boiler,  as  the  galvanic 
action  in  such  a  case  would  probably  soon  wear  the  points  of  contact  into  holes.  The 
platform  may  consist  of  three-inch  planking  laid  across  the  keelsons,  nailed  with  iron 
nails  the  heads  of  which  are  well  punched  down,  and  calked  and  puttied  like  a  deck. 
The  surface  may  then  be  painted  over  with  thin  putty,  and  fore-and-aft  boards  of  half 
the  thickness  may  then  be  laid  down  and  nailed  securely  with  iron  nails  having  the 
heads  well  punched  down.  This  platform  must  then  be  covered  thinly  and  evenly  with 
mastic  cement  and  the  boiler  be  set  down  upon  it,  and  the  cement  must  be  calked  be- 
neath the  boiler  by  means  of  wooden  calking-tools  so  as  completely  to  fill  every  vacuity. 
Coamings  of  wood  sloped  on  the  top  must  next  be  set  round  the  boiler,  and  the  space 
between  the  coamings  and  the  boiler  must  be  calked  full  of  cement,  and  be  smoothed 
off  on  the  top  to  the  slope  of  the  coamings,  so  as  to  throw  off  any  water  that  might  be 
disposed  to  enter  between  the  coamings  and  the  boiler." 

Ledieu  gives  the  following  compositions  for  the  cement  used  in  setting  boilers — viz., 
equal  quantities  of  whale-oil,  ox-blood,  and  powdered  unslaked  lime  ;  or,  Spanish  white, 
oil,  and  a  small  quantity  of  cow-hair. 

Hamelin's  mastic  cement  for  the  setting  of  boilers  is  compounded  as  follows:  "To 
any  given  weight  of  sand  or  pulverized  earthenware  add  two-thirds  such  given  weight 
of  powdered  Bath,  Portland,  or  similar  stone,  and  to  every  560  Ibs.  weight  of  the  mix- 
ture add  40  Ibs.  weight  of  litharge,  2  Ibs.  of  powdered  glass  or  flint,  1  Ib.  of  minium, 


313 


314  STEAM  BOILERS.  CHAP.  XIV. 

and  2  Ibs.  of  gray  oxide  of  lead ;  pass  the  mixture  through  a  sieve  and  keep  it  in  a 
powder  for  use.  When  wanted  for  use  a  sufficient  quantity  of  the  powder  is  mixed  with 
some  vegetable  oil  upon  a  board  or  in  a  trough  in  the  manner  of  mortar,  in  the  propor- 
tion of  605  Ibs.  of  the  powder  to  5  gallons  of  linseed,  walnut,  or  pink  oil,  and  the  mix- 
ture is  stirred  and  trodden  upon  until  it  assumes  the  appearance  of  moistened  sand, 
when  it  is  ready  for  use.  The  cement  should  be  used  on  the  same  day  that  the  oil  is 
added,  else  it  will  set  into  a  solid  mass."  (Bourne.} 

With  boilers  set  on  a  platform  in  the  above-described  manner  the  cement  is  apt  to 
crack  after  a  while  and  become  detached  from  the  shell  of  the  boiler,  and  when  leaks 
occur  in  the  bottom  of  the  boiler  the  water  spreads  over  the  platform  and  corrosion 
takes  place  over  a  large  surface  unnoticed.  Access  to  the  bottom  of  the  boiler  can  be 
had  only  by  cutting  away  portions  of  the  platform  from  below,  and  it  is  a  difficult  mat- 
ter to  locate  a  leak  in  the  bottom  of  the  boiler.  For  these  reasons  it  is  thought  prefer- 
able to  omit  the  platform  and  let  the  boiler  rest  directly  on  keelsons,  a  clear  passage,  ex- 
tending the  whole  length  of  the  boiler,  being  left  between  the  keelsons,  so  that  the  bot- 
tom of  the  boiler  may  be  examined,  cleaned,  painted,  and  repaired.  The  boiler  should 
be  placed  so  that  the  seams  connecting  the  front  and  back  to  the  bottom  are  acces- 
sible for  calking,  and  for  removing  and  replacing  rivets.  Boilers  must  never  be  set 
directly  on  oak  or  other  wood  containing  acids  which  corrode  iron,  but  a  cap-piece  of 
pine  rrmst  be  spiked  to  the  top  of  the  keelson. 

The  water-legs  of  dry -bottom  boilers  are  set  on  cast-iron  frames  or  saddles.  Figures 
3  and  4,  Plate  XXXI.,  illustrate  the  form  of  saddles  used  in  United  States  naval  vessels. 
The  ashpan  and  half  of  the  saddles  for  the  sides  and  back  of  each  furnace  are  fre- 
quently cast  in  one  piece.  When  they  are  made  in  separate  pieces  they  are  more 
easily  handled  in  case  it  is  necessary  to  remove  them  for  the  purpose  of  examining  or 
repairing  the  water-legs  without  moving  the  boiler  from  its  seat.  At  places  where  laps 
or  rivets  occur  on  the  water-legs  the  top  flange  of  the  saddle  is  cored  out  to  clear  them. 
All  spaces  between  the  water-leg  and  the  upper  flange  of  the  saddle  are  filled  with 
cement,  so  that  no  water  can  lodge  there.  When  dry-bottom  boilers  are  used  in  a 
wooden  vessel  precautions  have  to  be  taken  to  prevent  the  keelsons  and  the  lining  of 
the  vessel  being  set  on  fire  by  the  heat  radiated  through  the  interstices  of  the  grates  or 
by  the  fire  which  falls  in  cleaning  or  hauling  the  fires.  In  several  United  States  nav:il 
vessels  the  wooden  keelsons  are  protected  by  cast-iron  cap-pieces  on  which  the  saddles 
rest ;  an  air-space  is  formed  under  the  cast-iron  ashpan  by  corrugated  wrought-iron 
plates,  i  inch  thick,  resting  on  the  keelsons  and  on  ledges  formed  on  the  rib  which 
stiffens  the  bottom  of  the  ashpan. 


SEC.  2.  SETTING  AND  ERECTION  OF  BOILERS.  315 

The  arrangement  shown  in  figure  4,  Plate  XXXI.,  was  designed  for  U.  S.  S.  Yantic. 
The  bottom  of  each  ashpit  is  formed  by  a  shallow  tank  4  inches  deep,  built  of  f -inch 
wrought-iron  plates  and  stiffened  by  f-inch  socket-rivets  placed  9  inches  apart.  This 
tank  is  filled  with  cement,  which  must  be  poured  in  from  the  side  and  not  from  the 
top.  This  ashpan  rests  at  its  four  corners  on  cast-iron  blocks  8  inches  square,  which 
are  secured  by  a  large  wood-screw  to  the  keelsons.  The  saddles  rest  on  the  top  of  the 
ashpan  on  wrought-iron  strips,  and  the  sides  and  the  back  of  the  saddles  are  made  in 
separate  pieces.  This  arrangement  allows  any  of  the  saddles  to  be  removed  and  re- 
placed with  ease  without  raising  the  boiler  from  its  seat ;  and  after  removing  any  of  the 
saddles  the  corresponding  tank  on  which  they  rest  may  likewise  be  pulled  out  and 
replaced. 

Cylindrical  boilers  rest  on  saddles,  as  shown  on  Plate  XXX.  and  in  figure  2,  Plate 
XXXI.  These  saddles  are  either  made  of  cast-iron  or  are  built  up  of  wrought-iron  plates 
and  angle-irons.  In  wooden  vessels  they  are  secured  by  holding-down  bolts  to  the  keel- 
sons ;  in  iron  vessels  they  are  frequently  riveted  to  the  frames  of  the  hull. 

2.  Securing  Boilers. — To  prevent  the  boilers  from  shifting  or  moving  in  conse- 
quence of  the  violent  motions  of  the  vessel  in  a  sea-way,  they  are  securely  tied  to  the 
hull  of  the  vessel,  and  when  there  are  several  boilers  arranged  in  pairs  they  are  tied  at 
the  top  to  one  another.  No  part  of  the  boilers  rigidly  connected  with  the  shell  should 
be  attached  to  the  decks  of  the  vessel ;  on  the  contrary,  sufficient  clearance  must  be  left 
between  the  deck-beams  and  hatch-framing  and  the  boilers  to  allow  for  the  working  of 
the  ship  when  it  is  severely  strained.  The  longitudinal  or  pitching  motion  of  large  ves- 
sels is  not  sufficiently  violent  to  necessitate  special  precautions  for  holding  flat-bottomed 
boilers  in  their  seat.  To  guard  against  the  effect  of  the  transverse  or  rolling  motion  of 
the  vessel  the  boilers  are  tied  down  to  the  floor  of  the  vessel  by  wrought-iron  straps 
passing  diagonally  up  the  sides  of  the  boilers.  These  straps  are  secured  to  the  shell  by 
bolts  and  nuts ;  the  bolts  must  fit  accurately  the  holes  in  the  straps  and  in  the  shell. 

When  boilers  of  the  type  illustrated  on  Plates  VI.,  VII.,  and  XVII.,  in  which  the 
xiptake  forms  an  integral  part  of  the  shell,  are  arranged  in  pairs  opposite  to  one  another, 
they  are  sufficiently  tied  together  at  the  top  by  their  uptakes.  When  the  uptakes  are 
separate  structures,  built  on  the  shell  of  the  boilers,  the  latter  are  generally  tied  to  one 
another  at  the  top*  by  straps  or  braces.  In  U.  S.  S.  Trenton  each  pair  of  opposite 
boilers  is  tied  together  near  the  top  by  two  wrought-iron  straps,  1  inch  thick  and  4 
inches  wide,  extending  across  the  fire-room  immediately  below  the  uptakes.  Each  end 
of  these  straps  is  secured  to  the  cylindrical  shell  of  the  boilers  by  four  bolts  IJ  inches  in 
diameter.  The  cylindrical  boilers  of  U.  S.  S.  Nipsic  (see  Plate  XXX.)  are  secured  to 


316  STEAM  BOILERS. 


CHAP.  XIV. 


their  saddles  by  turned  bolts  passing  through  reamed  holes  in  the  shell ;  the  saddles  are 
held  by  composition  bolts  passing  through  the  frames  of  the  hull. 

In  other  vessels  each  cylindrical  boiler  is  held  down  in  the  saddles  by  four  wrought  - 
iron  braces,  one  being  placed  near  the  front  and  another  near  the  back  at  either  side  of 
the  boiler.  The  lower  end  of  each  brace  is  bolted  either  directly  to  the  hull  of  the  ves- 
sel or  to  the  saddle,  and  the  upper  end  is  secured  by  a  nut  to  a  lug  bolted  to  the  cylin- 
drical shell  of  the  boiler. 

3.  Erection  of  Boilers  in  the  Vessel. — In  preparing  the  bed  on  which  the 
boilers  or  their  saddles  are  to  rest,  the  boiler-keelsons  are  dubbed  off  to  lines  marked  on 
their  sides  representing  the  intersections  of  the  plane  of  the  bottom  of  the  boilers  or 
their  saddles  with  the  keelsons.  To  find  the  traces  of  this  plane  stretch  two  lines,  one 
at  the  after  end  and  one  at  the  forward  end  of  the  boiler-bed,  at  a  determined  height 
above  the  top  of  the  main  keelson,  and  at  right  angles  with  the  horizontal  centre  line  of 
the  main  keelson  and  with  perpendiculars  drawn  from  the  centre  line  of  the  deck  to  the 
centre  line  of  the  main  keelson  ;  then  measure  from  the  transverse  lines  the  distance  at 
which  the  bottom  of  the  boilers  or  their  saddles  should  be  placed  below  the  horizontal 
plane  passing  through  these  two  transverse  lines,  and  mark  the  points  thus  found  on 
the  sides  of  the  boiler-keelsons. 

In  case  the  boilers  are  to  be  set  on  a  platform  allowance  is  to  be  made  for  the  thick- 
ness of  the  planking  and  of  the  bed  of  cement,  and  the  platform  is  built  on  the  keelsons 
after  these  have  been  dubbed  off  to  the  proper  height. 

The  distance  of  the  centre  line  of  the  boilers  from  the  centre  line  of  the  engines  is 
measured  along  the  centre  line  of  the  main  keelson  according  to  the  dimensions  given 
on  the  drawing,  and  is  marked  on  the  keelsons  by  a  transverse  line  perpendicular  to  the 
centre  line  of  the  main  keelson.  The  location  of  each  boiler  is  then  determined  by 
measuring  the  distances  given  on  the  drawing  from  the  centre  line  of  the  main  keelson 
and  from  the  common  centre  line  of  the  boilers,  and  the  points  thus  found  are  marked 
on  the  boiler-keelsons  or  the  platform. 

In  case  saddles  are  used  for  the  boilers,  they  are  now  placed  in  position. 

After  these  preparations  are  made  the  boilers  are  put  aboard  by  means  of  a  crane  or 
shears.  When  the  boilers  are  slung  in  chains  the  corners  of  the  shell  must  be  protected 
by  chafing-gear  of  wood  and  mats.  The  boilers  are  put  aboard  without  the  furnace  and 
uptake  doors,  grate-bars,  valves,  and  other  removable  attachments ;  but  it  is  well  to 
keep  the  manholes  and  handholes  and  similar  openings  closed,  in  order  that  if  the 
slings  should  give  way  and  the  boiler  should  fall  overboard  it  would  not  fill  with 
water. 


SEC.  S.  SETTING  AND  ERECTION  OF  BOILERS.  317 

The  decks  are  left  open  sufficiently  to  allow  the  boilers  to  pass  through  them  ;  and 
the  deck-framing  around  the  boiler-hatches  is  arranged  in  such  a  manner  that  it  can  be 
taken  up  without  disturbing  the  deck-beams  when  the  boilers  are  to  be  hoisted  out  at  a 
future  time. 

The  first  boilers  to  be  put  aboard  are  those  which  are  to  be  situated-  at  the  extreme 
forward  and  after  ends  of  the  fire-room.  As  the  boiler  is  lowered  down  into  the  hold  of 
the  vessel  it  is  placed  on  blocks  or  rollers  ;  the  slings  passing  around  the  shell  are  then 
cast  off,  and  the  boiler  is  moved  by  means  of  tackle,  jacks,  or  other  appliances  into  its 
proper  position  corresponding  to  the  marks  on  the  keelsons,  and  then  it  is  gradually 
lowered  from  the  blocks  into  its  seat.  The  correctness  of  the  position  of  boilers  of  the 
type  represented  on  Plates  VI.,  VII. ,  XVII.  is  verified  by  seeing  that  the  upper  por- 
tions of  the  uptakes,  which  form  the  base  of  the  chimney,  meet  properly,  and  that  the 
centre  of  the  circle  formed  by  their  cross-section  falls  on  a  line  stretched  from  the  centre 
of  the  boiler-hatch  to  the  centre  line  of  the  main  keelson. 

• 

When  the  boilers  are  to  be  set  in  cement  on  a  platform,  they  must  now  be  raised  by 
jacks  from  their  seat  sufficiently  high  to  allow  men  to  crawl  under  them  and  spread  the 
cement  evenly  over  the  platform  ;  during  this  process  the  boilers  are  supported  at  the 
four  corners  by  blocks  of  wood.  After  the  bed  of  cement  has  been  laid  the  boilers  are 
lowered  carefully  into  position. 

Boilers  which  are  to  rest  on  saddles  are  first  placed  on  blocking  directly  over  their 
saddles ;  after  the  correctness  of  their  position  relatively  to  each  other  and  to  their 
saddles  has  been  verified  they  are  lowered  carefully  into  their  seat. 

The  straps  which  are  to  tie  the  boilers  to  the  hull  of  the  vessel  and  to  one  another  are 
now  fitted  and  secured  to  them,  and  the  uptakes  which  are  built  in  the  boilers  are 
riveted  together  where  they  meet  at  the  top.  With  cylindrical  boilers  the  construction 
of  the  smoke-boxes  and  uptakes  commences  now.  The  grates,  doors,  valves,  and  other 
fixtures  are  attached  to  the  boilers  as  soon  as  these  are  placed  permanently  in  position. 
The  pipes  connecting  the  boilers  with  the  outboard- valves,  the  pumps,  and  the  main  en- 
gines are  next  put  up ;  the  exact  length,  shape,  and  position  of  these  pipes  is  deter- 
mined by  making  board  templates  after  the  boilers  are  placed  in  position,  care  being 
taken  that  the  cocks  and  valves  attached  to  them  are  accessible,  that  one  pipe  may  be 
taken  down  without  removing  another  one,  that  the  bends  of  the  pipes  form  easy  curves, 
and  that  the  pipes  follow  the  most  direct  course  compatible  with  the  foregoing  con- 
ditions. 

Finally,  the  felting  and  other  covering  is  placed  over  the  boiler-shells  and  the 
pipes. 


318  STEAM  BOILERS. 


CHAP.  XIV. 


As  soon  as  the  uptakes  are  constructed,  and  the  deck  around  the  boiler-hatch  has 
been  completed,  the  chimney  and  the  escape-pipe  are  hoisted  aboard  and  placed  in 
position,  and  the  hatch-gratings,  plates,  ventilators,  etc.,  are  put  up.  In  slinging  the 
smoke-pipe  for  hoisting  it  must  be  stiffened  by  temporary  wooden  stays  placed  inside, 
or  by  boards  placed  outside  between  the  slings  and  the  pipe. 


CHAPTER  XY. 

BOILER   MOUNTINGS  AND  ATTACHMENTS. 

1.  Grate. — The  grate  of  furnaces  in  which  coal  is  burnt  is  composed  of  alternate 
bars  and  spaces. 

In  many  boilers  the  front  part  of  the  grate  is  formed  by  a  horizontal  or  slightly  in- 
clined iron  plate  without  perforations,  about  20  inches  long ;  this  is  called  the  dead- 
plate  or  dumb-plate.  It  was  introduced  by  Watt,  and  is  used  especially  in  furnaces 
where  bituminous  coal  is  used  as  fuel.  In  firing  the  coal  is  thrown  first  on  the  dead- 
plate,  where  the  radiant  heat  of  the  fire  volatilizes  the  hydrocarbons  ;  and  after  the  coal 
is  thus  reduced  to  coke  it  is  pushed  inwards  and  spread  over  the  fire.  In  the  boilers 
of  United  States  naval  vessels  the  dead-place  is  omitted. 

The  grate-bars  are  ordinarily  placed  lengthwise  the  furnace  and  rest  on  supports  at 
the  front  and  back  of  the  furnace,  and,  when  the  grate  is  long,  on  one  or  two  interme- 
diate cross-bars.  The  bars  must  be  strong  enough  to  bear  the  weight  of  the  fuel  and  to 
withstand  the  rough  usage  to  which  they  are  unavoidably  subjected  in  working  the  fire. 
They  must  rest  securely  on  their  supports,  but  must  be  allowed  to  expand  and  contract 
freely  with  the  great  variations  of  temperature  to  which  they  are  exposed. 

The  overheating  of  the  bars  is  prevented  by  the  rapid  currents  of  air  rushing  to  the 
bed  of  fuel  through  the  spaces  between  the  bars,  and  by  a  thin  layer  of  ashes  accu- 
mulating on  the  top  of  the  bars.  The  overheating  of  bars  may  be  due  to  their  faulty 
form,  or  to  obstructions  in  the  spaces  preventing  the  free  inflow  of  air,  or  to  the  intensity 
of  the  fire  ;  in  such  cases  the  bars  will  bend  and  warp  and  partially  melt  on  the  top. 

Coals  containing  sulphur  or  forming  easily-fused  clinker  destroy  the  bars  rapidly ; 
the  clinker  sticks  between  the  bars  and  obstructs  the  air-passages. 

The  top  of  the  grate  should  always  form  a  level  surface  flush  with  the  bottom  of  the 
opening  of  the  furnace-door ;  the  bars  which  project  above  the  level  of  the  grate  are 
liable  to  be  burnt  and  to  be  displaced  in  working  the  fire. 

Grate-bars  have  been  made  hollow  to  allow  a  current  of  air  or  water  to  pass  through 
them,  for  the  purpose  of  increasing  their  durability  and  adding  to  the  efficiency  of  the 


319 


320  STEAM  BOILERS.  CHAP.  XV. 

furnace ;  but  the  cost  of  such  contrivances  and  the  difficulty  of  keeping  them  in  order 
have  caused  their  rejection. 

In  marine  boilers  the  grate  generally  slopes  downward  from  the  furnace-mouth  to 
the  bridge- wall.  By  this  means  the  back  of  the  grate  is  more  easily  kept  covered  with 
fuel,  and  the  coal  is  prevented  in  a  measure  from  falling  out  of  the  furnace  into  the  fire- 
room  when  the  ship  rolls  and  the  door  is  open.  The  rate  of  this  slope  varies  from  one 
in  ten  to  one  in  twenty,  and  is  limited  by  the  heights  required  over  the  top  of  the  grate 
at  the  furnace-mouth  for  proper  firing,  and  below  the  grate  at  the  bridge  for  admitting  a 
sufficient  amount  of  air  and  for  working  the  fire  from  the  ashpit. 

Grate-bars  are  usually  made  of  cast-iron.  Wrought-iron  bars  are  frequently  used 
in  the  boilers  of  locomotives,  and  are  also  not  unf requently  used  in  marine  boilers  ;  they 
bend  and  warp  easily,  but  can  be  straightened  ;  they  are  not  so  easily  broken  or  fused 
and  burnt  as  cast-iron  bars,  and  they  may  be  made  somewhat  lighter  than  the  latter. 
For  these  reasons  wrought-iron  bars  are  probably  cheaper  in  the  end,  although  their 
first  cost  is  greater  than  that  of  cast-iron  bars.  Wrought-iron  bars  are  most  simply 
made  by  riveting  two  plain  bars  together,  with  thimbles  between  them  for  distance- 
pieces  at  the  ends  and  in  the  middle,  and  letting  the  heads  of  the  rivets  determine  the 
width  of  the  space  between  two  adjacent  double  bars. 

The  length  of  grate-bars  should  not  much  exceed  three  feet.  According  to  Ledieu, 
the  grate-bars  of  French  naval  boilers  are  usually  made  of  wrought-iron,  and  29£  inches 
or  21f  inches  long,  according  to  the  length  of  the  grate.  Short  bars  are  more  easily 
handled  than  long  ones,  and  are  twisted  less  out  of  shape  by  overheating. 

Fi    133_  Various  shapes    have   been   given    to  grate-bars 

fatiaaaaalfail       mainly  with    a   view    to    increase  their  durability. 
nirijljliiijl       Figure  133  represents  the  top  and  bottom  views  of 
uuiluuujj       a  grate-bar  in  common  use,  designed  to  be  free  from  a 
tendency  to  warp  on  account  of  its  peculiar  shape. 

The  cast-iron  bars  generally  used  in  United  States  naval  boilers  are  illustrated  on 
Plate  XIX.  These  grate-bars  are  usually  made  from  f  inch  to  f  inch  wide  on  the  top. 
At  the  bottom  they  should  be  made  as  thin  as  they  can  be  cast,  and  the  necessary 
strength  should  be  obtained  by  proportioning  their  depth  to  their  length.  Thin  and 
deep  bars  are  less  liable  to  warping  than  thicker  and  less  deep  bars,  because  the  inflow- 
ing air  abstracts  the  heat  more  readily  from  them.  Grate-bars  are  generally  made 
from  J  inch  to  f  inch  thick  at  the  bottom,  and  from  3,  inches  to  3f  inches  deep  in  the 
middle  of  their  length.  The  outline  of  the  bottom  has  approximately  the  form  of  a 
parabola. 


SBC.  1.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  321 

Grate-bars  have  sometimes  a  uniform  width,  for  a  depth  of  about  f  inch  from  the  top, 
and  below  that  depth  a  rib  of  diminished  but  uniform  thickness  ;  it  is,  however,  prefer- 
able to  let  them  taper  evenly  from  the  top  to  the  bottom,  as  such  a  form  facilitates  the 
flow  of  air  to  the  fuel,  the  fall  of  refuse  matter  through  the  grate,  and  the  pricking  of 
the  fire  from  below. 

At  each  side  of  the  ends  of  the  bars  projections  are  formed  which  determine  the  width 
of  the  spaces  between  them.  When  the  length  of  bars  exceeds  30  inches  similar  pro- 
jections are  formed  midway  between  their  ends  to  increase  their  lateral  stiffness.  Grate- 
bars  are  generally  made  double,  so  that  two  bars  with  the  proper  space  between  them 
form  one  piece  ;  this  saves  time  in  removing  and  replacing  them,  and  increases  greatly 
their  stiffness.  A  number  of  single  bars  are  provided  with  the  double  bars,  so  that  the 
whole  width  of  the  furnaces  may  be  filled  by  the  bars  without  jamming  them  and  with 
the  proper  spaces  between  them. 

The  following  considerations  govern  the  width  of  the  spaces  between  the  bars  :  a  suf- 
ficient quantity  of  air  must  be  admitted  to  the  fuel ;  the  spaces  must  not  be  obstructed 
too  easily  by  clinkers ;  the  prick-bar  must  pass  through  them  to  free  the  bottom  of  the 
bed  of  fuel  from  ashes  ;  on  the  other  hand,  the  coal  used  as  fuel  must  not  drop  through 
them,  therefore  small,  free-burning  coal  requires  narrower  spaces  than  lump  coal  and 
caking  coal.  The  width  of  the  clear  space  between  two  bars  is  usually  T\  inch  or 
i  inch  when  good  semi-bituminous  coal  is  used ;  with  anthracite,  and  with  coals  that 
cake  much  or  yield  large  quantities  of  ash  and  clinker,  the  space  is  made  £  inch  wide, 
and  sometimes  even  more. 

All  cast-iron  bars  used  in  United  States  naval  vessels  have  a  shallow  groove  on  the 
top  ;  the  ashes  which  accumulate  in  these  grooves  prevent  clinkers  from  adhering  to  the 
bars,  and  the  latter  are  less  easily  burnt. 

The  grate-bars  rest  with  their  ends  on  cross-bearers  or  bearing-bars,  and  they  are 
allowed  to  expand  freely  in  the  direction  of  their  length.  The  front  end  of  each  bar  is 
often  provided  with  a  lug  at  the  bottom,  which  hooks  on  the  bearing-bar  and  limits  the 
motion  of  that  end  of  the  bar ;  this  lessens  the  chance  of  the  bar  sliding  off  its  seat 
when  it  becomes  shortened  by  warping.  The  space  allowed  for  expansion  at  the  ends  of 
bars  is  frequently  insufficient ;  it  should  not  be  less  than  the  width  of  the  air-spaces  be- 
tween the  bars. 

To  prevent  coal  or  clinker  from  lodging  tightly  between  the  ends  of  bars  the  ends 
are  often  made  slanting,  either  at  the  top  or  at  the  bottom,  instead  of  square.  Some- 
times one  end  of  the  bars  is  made  tapering  and  rests  on  an  inclined  seat  (see  Plate  XY.) ; 
this  arrangement  allows  the  bars  to  expand  freely ;  but  the  bars  are  apt  to  be  raised 


322 


STEAM  BOILERS. 


CHAP.  XV. 


above  the  level  of  the  grate,  and,  in  consequence,  to  be  burnt  or  become  displaced  in 
cleaning  the  fires. 

The  bearing-bars  are  made  either  of  cast-iron  or  of  wrought-iron,  and  rest  with  their 
ends  on  lugs  attached  by  bolts  to  the  sides  of  the  furnace  (see  Plate  XIX.) 

The  middle  bearing-bar  is  made  double,  with  a  wide  space  to  let  ashes  and  clinker 
fall  through. 

The  front  bearing-bar  is  secured  by  a  few  large  bolts  to  the  furnace  door-frame ;  or, 
when  a  dead-plate  is  provided,  it  serves  as  a  support  for  the  front  end  of  the  grate- 
bars. 

The  back  bearing-bar  rests  on  lugs  bolted  to  the  water-bridge,  and  is  provided  with  a 
lug  at  each  end  in  order  to  maintain  an  air-space  between  the  bar  and  the  bridge-wall. 
When  the  bridge-wall  consists  of  a  separate  iron  frame  supporting  a  wall  of  fire-brick 
the  back  end  of  the  grate-bars  rests  on  a  ledge  formed  on  the  frame  of  the  bridge-wall. 

2.  Moving-grates. — In  order  to  diminish  the  labor  of  attending  to  the  fires  and  the 


Fig.  134, 


loss  in  efficiency  of  boilers  due  to  the  open- 
ing of  the  furnace-doors  for  supplying  the 
fuel  and  cleaning  the  fires,  various  contri- 
vances have  been  made  for  supplying  fuel 
to  furnaces  evenly  and  continuously  by 
mechanism.  Circular  revolving  grates 
turning  slowly  about  their  centre,  and 
grates  consisting  of  an  endless  web  of  short 
bars  moving  on  horizontal  rollers,  and  tra- 
velling from  the  furnace-mouth  to  the 
bridge  and  returning  through  the  ashpit, 
have  been  used  ;  but  none  of  these  contri- 
vances have  been  successfully  applied  to 
marine  boilers. 

In  other  forms  of  moving-grates  ap- 
plied to  marine  boilers  a  short,  reciprocat- 
ing motion  up  and  down,  or  from  side  to 
side,  may  be  given  to  the  grate-bars,  in 

order  to  keep  the  grate  clear  of  ashes  and  clinker  without  opening  the  furnace-door 

and  using  fire-tools. 

The  Murphy  shaking-grate  (see  figure  134)  consists  of  alternate  stationary  and 

vibrating  bars  placed  at  right  angles  to  the  length  of  the  furnace.    There  are  two  sets  of 


SEC.  2.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  323 

bars,  forming  two  inclined  planes,  sloping  downward  from  the  sides  of  the  furnace  to 
the  centre.  The  stationary  bars  rest  with  their  upper  ends  against  the  sides  of  the  fur- 
nace and  with  their  lower  ends  on  a  cast-iron  frame  consisting  of  two  parallel  bars 
extending  through  the  length  of  the  furnace,  supported  by  suitable  brackets.  The 
vibrating  bars  are  pivoted  at  their  upper  ends  to  the  upper  ends  of  the  stationary 
bare,  and  their  lower  ends  rest  against  the  continuous  feather  of  a  horizontal  bar  lying 
lengthwise  the  furnace  in  pillow-blocks  placed  at  the  front  and  back  of  the  furnace ; 
there  are  two  of  these  horizontal  bars,  one  for  each  side  of  the  grate.  By  rocking  the 
horizontal  bar  forward  and  back  on  its  axis  by  means  of  a  lever  attached  to  the  end 
protruding  from  the  ashpit  into  the  fire-room,  the  pivoted  bars  receive  a  vibrating  mo- 
tion, their  lower  ends  being  forced  alternately  above  and  below  the  level  of  the  station- 
ary bars. 

At  the  bottom  of  the  two  inclined  planes  of  the  grate,  and  entirely  independent  of  it, 
is  a  horizontal  bar,  3  inches  in  diameter,  lying  lengthwise  the  furnace  in  five  pillow- 
blocks  attached  to  the  central  frame.  This  bar  bristles  with  eight  rows  of  projecting 
teeth,  forming  cubes  of  one  inch  a  side.  This  bar  may  be  rocked  forward  and  back,  or 
revolved  entirely  around  its  axis,  by  a  lever  attached  to  the  end  protruding  into  the 
fire-room.  This  is  called  the  clinker-crusher  and  refuse-remover. 

In  firing  the  coal  is  thrown  along  the  upper  ends  of  the  grate-bars  solely,  and  slides 
downward  by  gravity  over  the  grate-surface  as  the  coal  on  the  latter  is  consumed.  An 
occasional  shaking  of  the  grate  by  the  vibrating  bars  accelerates  the  descent  of  the  coal, 
removes  from  it  such  refuse  as  can  fall  between  the  grate-bars,  and  prevents  the  occur- 
rence of  holes  in  the  fire.  Such  of  the  refuse  from  the  coal  as  cannot  pass  through  the 
spaces  between  the  grate-bars  slides  down  the  grate-surface  by  gravity,  and  is  broken  up 
and  worked  into  the  ashpit  by  the  vibratory  motion  of  the  clinker-crusher.  The  fires 
are  thus  kept  clean  and  free  of  holes  without  the  employment  of  fire-tools,  and  the  fur- 
nace-doors are  only  opened  for  throwing  in  the  coal. 

The  weight  of  this  grate  is  about  double  the  weight  of  the  ordinary  grate. 

Experiments  made  by  a  board  of  United  States  naval  engineers  to  determine  the 
efficiency  of  the  Murphy  grate  showed  that,  compared  with  the  ordinary  grate,  the 
economic  gain  due  to  its  use  was  in  direct  proportion  to  the  per  centum  of  refuse  re- 
moved through  the  furnace-door  with  the  ordinary  grate  in  use.  (See  section  13,  chap- 
ter ii.,  and  '  Report  on  the  Murphy  Grate-bar,  by  a  Board  of  United  States  Naval 
Engineers,  June  25,  1878.') 

The  Martin  or  Ashcroft  grate  (see  figure  135)  is  formed  by  wrought-iron  bars,  1£ 
inches  square  in  cross-section,  extending  the  whole  length  of  the  fiirnace  and  projecting 


324  STEAM  BOILERS.  CHAP.  XV. 

5  or  6  inches  beyond  the  front  of  the  boiler.  These  grate-bars  rest  on  wrought-iron 
bearing-bars  placed  about  18  inches  apart  and  supported  at  the  ends  by  lugs  bolted  to 
the  sides  of  the  furnace.  The  upper  side  of  the  bearing-bars  is  either  bevelled  to  a 
knife-edge  or  it  is  crenated  into  semicircles,  in  which  the  grate-bars  rest  and  from 
which  they  cannot  be  displaced  in  turning.  The  bars  are  revolved  by  means  of  a 
socket- wrench  applied  to  their  ends,  and  the  fire  is  thus  to  be  cleaned  from  ash  and 
clinker  without  opening  the  furnace-door  ;  but  no  thorough  cleaning  of  the  fires  can  be 
made  by  merely  revolving  the  grate-bars,  which  by  a  few  turns  cut  out  grooves  in  the 
fires  and  leave  the  coherent  mass  above  untouched.  (See  '  JZeport  on  AsTicroft  Furnace- 
doors  and  Grate-bars,  by  a  Board  of  United  States  Naval  Engineers,  March  27, 1878.') 

3.  Bridge-walls. — The  bridge  is  a  wall  or  partition  near  the  back  of  the  furnace 
which  limits  the  length  of  the  grate  and  forms  an  abutment  for  the  bed  of  fuel.  The 
height  of  the  bridge-wall  regulates  the  area  of  the  passage  leading  from  the  furnace  to 
the  combustion-chamber  or  back-connection,  and  affects  greatly  the  efficiency  of  boilers, 
through  the  influence  which  it  exerts  on  the  amount  of  air  admitted  to  the  furnace  and 
on  the  thorough  mixing  of  the  gases  during  combustion.  (See  section  5,  chapter  mi.} 

The  bridge  is  often  formed  by  a  hollow  wall  communicating  with  the  water-space  of 
the  boiler  and  forming  an  integral  part  of  the  latter  (see  section  7,  chapter  ix.),  or  it  is 
formed  by  a  wall  of  fire-brick.  Sometimes  a  solid  mass  of  fire-brick  fills  the  back  of  the 
furnace  behind  the  grate  ;  but  this  arrangement  is  objectionable,  because  it  hides  leaks 
which  may  occur  there.  The  bridge-wall  consists  usually  of  a  vertical  cast-iron  frame 
resting  on  the  bottom  and  bolted  by  means  of  flanges  or  straps  to  the  sides  of  the  fur- 
nace, or  of  a  horizontal  plate  extending  from  the  back  of  the  grate  to  the  back  of  the 
furnace,  and  resting  on  brackets  or  angle-irons  bolted  to  the  sides  of  the  furnace  ;  this 
frame  or  plate  supports  the  back  end  of  the  grate-bars  and,  behind  them,  a  wall  of  fire- 
brick (see  Plate  XII.) 

The  bridge-wall  is  often  provided  with  openings  for  admitting  jets  of  air  to  the  com- 
bustion-chamber or  back-connection,  the  supply  of  air  being  regulated  by  a  register  or 
by  a  hinged  valve,  the  position  of  which  can  be  adjusted  by  means  of  a  rod  and  suitable 
connections  from  the  fire-room  (see  Plate  XV.)  Such  openings  in  the  bridge- wall  are 
now  always  omitted  in  the  boilers  of  United  States  naval  vessels,  since  repeated  experi- 
ments have  demonstrated  that  an  air-admission  to  the  back-connection  produces  no  use- 
ful results  when  anthracite  coal  is  used  as  fuel.  In  English  and  French  boilers  designed 
to  burn  bituminous  coal  the  bridge-wall  is  always  provided  with  openings  for  air-admis- 
sion. Specifications  issued  by  the  Admiralty  for  boilers  for  English  naval  vessels 
require  an  aggregate  area  of  not  less  than  three  square  inches  of  opening  in  the  bridge 


SEC.  4  BOILER  MOUNTINGS  AND  ATTACHMENTS.  325 

for  the  admission  of  air  to  the  back-connection  for  each  square  foot  of  grate-surface. 
(See  section  11,  chapter  mi.} 

4.  Fumaee-doors  and  Door-frames. — The  furnace-door  opening  in  marine  boil- 
ers having  grates  of  the  usual  dimensions  is  ordinarily  from  14  inches  to  16  inches  high 
and  from  18  inches  to  20  inches  wide,  the  upper  part  being  arched  and  the  lower  part 
square. 

In  the  rectangular  boilers  of  United  States  naval  vessels  the  furnace-door  openings 
are  constructed  in  the  front  wall  of  the  boiler  in  the  manner  shown  on  Plates  VI.,  VII., 
and  XVII.  When  cast-iron  furnace-doors  are  used  the  opening  is  surrounded  by  a  cast- 
iron  frame  bolted  by  five  or  six  |-inch  bolts  to  the  boiler-front.  On  this  frame  are  cast 
the  catch  and  the  hinges  for  the  door  and  the  sill-plate  ;  the  frame  is  fitted  to  the  boiler- 
front  by  means  of  a  narrow  chipping-strip  surrounding  its  outer  circumference,  and 
around  the  door-opening  it  has  another  chipping-strip,  against  which  the  door  is 
fitted. 

When  the  furnace-doors  are  made  of  wrought-iron,  door-frames  are  dispensed  with, 
the  doors  being  made  to  fit  directly  against  the  boiler-front  and  the  sill-plate.  The 
latter  is  made  either  of  wrought-iron  or  cast-iron,  and  is  bolted  in  place  as  shown  on 
Plate  XIX.  The  top  of  the  sill-plate  is  level  with  the  top  of  the  front  of  the  grate,  and 
it  has  a  flange  to  which  the  front  bearing-bar  is  bolted  or  riveted. 

When  the  furnace  is  secured  to  the  boiler-front  in  the  manner  shown  in  figure  96 
and  on  Plates  VIII. ,  XL,  and  XII.,  a  frame  is  bolted  in  the  furnace-mouth,  to  which 
the  furnace-door  is  fitted  (see  Plate  XXIX.)  This  frame  consists  of  a  single  casting 
about  6  inches  deep,  to  which  at  the  front  and  back  wrought-iron  plates  f  inch  thick 
are  bolted,  thus  forming  a  double  wall  which  intercepts  the  heat  radiated  from  the 
incandescent  fuel.  The  front  plate  is  provided  with  a  few  holes  about  1  inch  in  diame- 
ter, and  the  back  plate  is  perforated  with  numerous  holes  J  inch  or  ^  inch  in  diameter. 
The  catch  and  hinges  for  the  furnace-door  are  riveted  to  the  front  plate  of  the  door- 
frame. 

The  wrought-iron  furnace-doors  of  boilers  of  United  States  naval  vessels  consist  of  a 
front  plate  provided  with  about  fifteen  1-inch  holes,  and  stiffened  by  a  lip  turned  up 
around  its  circumference  which  fits  against  the  boiler-front ;  and  of  a  back  plate,  which 
has  flanges  aboiit  2|  inches  deep  turned  up  around  its  circumference,  and  is  perforated 
with  numerous  J-inch  or  ^-inch  holes.  The  two  plates  are  made  of  J-inch  boiler-iron, 
and  are  tied  together  by  four  f-inch  socket-rivets  (see  Plates  XIX.  and  XXIX.) 

Cast-iron  furnace-doors  have  a  similar  box-form  ;  the  front  and  sides  are  cast  in  one 
piece  about  £  inch  thick,  and  a  wrought-iron  or  cast-iron  screen-plate,  perforated  with 


326 


STEAM  BOILERS. 


CHAP.  XV. 


numerous  small  holes,  is  bolted  to  tlie  back,  lugs  being  cast  on  the  sides  for  securing  it. 
The  hinges  are  cast  on  the  front  plate,  which  is  also  provided  with  a  number  of  large 
holes  for  the  admission  of  air.  The  hinges  of  furnace-doors  are  made  frequently  of 
composition. 

The  Martin  or  Ashcroft  furnace-door  (see  figure  135),  which  has  been  fitted  to  a 

number  of  boilers  of  United 
States  naval  vessels,  con- 
sists of  a  square  wrought- 
iron  plate,  slightly  concave 
on  the  inward  side,  which 
is  hung  from  a  horizontal 
axis  fixed  to  the  upper 
edge  of  the  door.  This 
axis  rests  on  brackets  at- 
tached to  the  cast-iron  fur- 
nace door-frame  at  each 
side  of  the  furnace-mouth, 
and  is  provided  with  coun- 
terbalances which  are  to 
keep  the  door  in  any  position  in  which  it  may  be  placed.  After  a  series  of  competitive 
trials  with  the  Martin  door  and  the  ordinary  furnace-door,  the  former  was  condemned 
by  a  board  of  naval  engineers  as  possessing  none  of  the  practical  and  economical  advan- 
tages claimed  by  the  patentee,  and  offering,  on  the  contrary,  serious  inconveniences  in 
managing  the  fires.  (See  '  Report  on  AsJicroft  Furnace-door  and  Grate-bar  by  a  Board 
of  United  States  Naval  Engineers.'} 

In  order  to  intercept  more  completely  the  heat  radiated  from  the  bed  of  incan- 
descent fuel  and  communicate  it  to  the  entering  air,  several  sheets  of  wire  gauze  have 
sometimes  been  placed  between  the  perforated  front  and  back  plates  of  the  furnace- 
door. 

"The  most  complete  apparatus  for  intercepting  the  heat  radiated  to  the  furnace-door 
is  that  of  Mr.  Prideaux,  which  consists  of  three  gratings,  each  made  of  a  series  of  thin 
iron  plates  set  edgeways,  with  narrow  passages  between  them  for  the  entering  streams 
of  air.  The  radiant  heat  is  completely  intercepted  by  placing  two  of  those  sets  of  plates 
with  opposite  obliquities,  and  the  third  parallel  to  the  sides  of  the  furnace  mouth- 
piece." (RanMne.} 

To  regulate  the  admission  of  air  through  the  door  to  the  furnace  Prideaux  made  the 


SEC.  5.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  327 

gratings  movable  like  Venetian  blinds ;  a  self-acting  mechanism  opened  them  when 
fresh  coal  was  supplied,  and  gradually  closed  them  as  the  fuel  became  converted  into 
coke.  The  openings  in  the  ordinary  furnace-door  are  frequently  provided  with  a  regis- 
ter, by  means  of  which  the  air-admission  can  be  regulated  by  hand. 

According  to  Rankine  the  total  area  of  the  perforations  in  the  furnace-door,  in  recent 
English  examples,  is  ^  of  the  area  of  the  grate  when  25  pounds  of  bituminous  coal  are 
burnt  per  square  foot  of  grate  per  hour.  In  United  States  naval  boilers,  burning  from 
12  to  16  pounds  of  anthracite  per  square  foot  of  grate  per  hour,  the  aggregate  area  of 
the  openings  in  the  furnace-doors  varies  between  £  square  inch  and  1  square  inch  per 
square  foot  of  grate. 

5.  Connection-doors,  Ashpit-doors,  and  Ashpans. — Cast-iron  connection-doors 
are  at  present  superseded  by  wrought-iron  ones,  which  are  fitted  without  door-frames 
directly  to  the  front  of  the  boiler.  The  hinges  are  often  made  of  composition,  and  are 
placed  either  at  the  top  or  at  one  side  of  the  door. 

To  diminish  the  radiation  of  heat  from  the  large  surfaces  of  these  doors  a  shield- 
plate  is  secured  to  the  door-plate  by  means  of  socket-rivets,  leaving  a  space  of  two  or 
three  inches  between  the  two  plates.  This  shield-plate  is  placed  either  on  the  inside  or 
the  outside  of  the  door-plate,  and  in  some  cases  two  shield-plates,  an  inner  and  an  outer 
one,  are  employed. 

The  connection-doors  of  United  States  naval  boilers  (see  Plates  XIX.  and  XXIX.) 
are  made  double,  of  J-inch  plate-iron,  stayed  by  socket-bolts ;  the  outer  plate  is  stif- 
fened by  a  lip  turned  up  around  its  circumference,  the  edge  of  which  fits  closely  against 
the  front  of  the  boiler ;  the  edges  of  the  inner  flanged  plate  form  a  well-fitting  joint  on 
the  outer  plate.  The  space  between  the  two  plates  is  sometimes  filled  with  a  non-con- 
ducting material,  as  plaster-of- Paris,  but  this  makes  the  door  heavy.  On  this  account 
the  dead  air  in  the  space  is  generally  relied  on  as  a  non-conductor. 

Ashpit-doors  are  used  to  check  the  draught  in  order  to  diminish  the  rate  of  com- 
bustion, and  to  prevent  the  inflow  of  cold  air  through  furnaces  which  are  not  in  use. 
They  should  be  made  to  fit  close  and  to  be  easily  opened  and  shut. 

Sometimes  the  door  consists  of  a  simple  plate  placed  in  the  mouth  of  the  ashpit, 
which  turns  on  a  horizontal  axis  passing  through  the  middle  of  the  plate  (like  a  damper), 
catches  being  provided  to  secure  the  plate  in  any  desired  position. 

Wrought-iron  or  cast-iron  doors,  opening  in  halves  and  hinged  on  either  side  of  the 
ashpit,  are  frequently  used.  In  such  cases  a  cast-iron  or  angle-iron  frame  is  secured  by 
bolts  to  the  boiler-front  around  the  ashpit-opening,  and  the  doors  are  provided  with 
openings  and  a  register  for  regulating  the  admission  of  small  quantities  of  air  to  the 


328  STEAM  BOILERS.  CHAP.  XV. 

ashpit.  Such  hinged  doors  are  generally  used  when  air  is  forced  into  the  ashpits  by 
means  of  a  fan-blower. 

In  boilers  of  United  States  naval  vessels  the  ashpit-doors  are  now  made  always  of  a 
single  wrought-iron  plate,  i  inch  or  ^  inch  thick,  stiffened  by  a  lip  turned  up  around 
its  circumference.  The  edge  of  this  lip  fits  directly  against  the  front  of  the  boiler. 
The  construction  and  manner  of  securing  these  doors  are  illustrated  on  Plates  XIX. 
and  XXIX.  When  the  ashpits  are  to  be  kept  wide  open  the  doors  are  lifted  off  their 
catches  and  hung  upon  hooks  permanently  attached  to  the  connection-doors. 

In  dry-bottom  boilers  cast-iron  or  wrought-iron  asJipans  are  used  which  are  remova- 
ble and  are  intended  to  contain  water.  Wrought-iron  ashpans  are  made  of  J-inch  or 
f-inch  iron,  of  a  single  plate,  with  a  flange  turned  up  around  the  sides  and  back.  The 
front  slopes  gradually  up  to  the  height  of  the  flange  to  facilitate  the  hauling  of  the 
ashes.  The  bottom  of  the  pans  may  be  stiffened  by  two  or  three  angle-irons  running  in 
a  longitudinal  direction. 

False  asJipans  are  sometimes  used  to  protect  the  iron  and  the  stay-bolt  heads  of 
water-bottoms  from  the  corroding  effect  of  wet  ashes  and  from  rough  usage  in  hauling 
ashes.  They  are  made  of  wrought-iron,  having  a  lip  a  couple  of  inches  high  turned  up 
on  each  side,  and  in  front  a  lip  turned  down  which  laps  over  the  ledge  of  the  floor-plates. 

6.  Manhole  and  Handhole  Plates. — Manholes  giving  access  to  the  interior  of 
the  boiler  are  cut  in  the  front  of  the  boiler  in  the  spandrels  between  the  furnaces,  be- 
sides one  or  two  near  the  top  of  the  boiler  leading  into  the  steam-space. 

Handholes  or  mudholes  are  cut  in  the  water-legs  near  the  bottom  in  the  front  and 
back  of  the  boiler,  and  at  other  convenient  places,  for  scaling,  cleaning,  and  washing  out 
the  boiler. 

Manhole  and  handhole  plates  should  always  be  put  on  the  inside  of  the  boiler,  so 
that  the  steam-pressure  tends  to  tighten  the  joint  and  keep  the  plate  in  position  in  case 
the  threads  of  the  bolts  which  secure  the  plates  should  be  stripped. 

Manholes  and  handholes  are  generally  made  oval  in  shape,  of  such  proportions  that 
the  smallest  diameter  of  the  plate  is  somewhat  less  than  the  largest  diameter  of  the 
hole.  Where  practicable  the  largest  and  smallest  diameters  of  manholes  are  made 
about  15  inches  and  12  inches  respectively.  When  the  space  in  the  spandrels  between 
the  furnaces  does  not  admit  of  cutting  oval  holes  of  sufficiently  large  size  the  holes  are 
often  triangular  in  shape.  In  cylindrical  shells  manholes  shotild  be  cut  in  such  a  way 
that  their  shorter  axis  lies  in  the  longitudinal  direction  of  the  shell,  so  that  the  least 
quantity  of  metal  is  removed  in  the  line  where  the  greatest  strain  obtains. 

A  flat,  welded  wrought-iron  ring,  about  3  inches  wide,  is  riveted  around  manholes 


SEC.  6.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  329 

« 

inside  the  boiler  and  calked  tight,  the  rivet-heads  being  countersunk.  The  practice  of 
putting  this  ring  outside  the  boiler,  preTailing  still  to  a  great  extent  in  England,  is  wrong  ; 
for  the  ring  gives  not  only  stiffness  to  the  boiler-plate  but  protects  it  inside  the  boiler 
from  corrosion,  which  is  often  very  active  in  the  vicinity  of  manholes  and  mudholes. 
Cast-iron  rings  are  sometimes  used  instead  of  wrought-iron  ones ;  but  especially  on 
cylindrical  shells,  where  these  rings  have  to  restore  the  strength  lost  by  cutting  the 
openings,  cast-iron  rings  do  not  answer  the  purpose  on  account  of  the  difference  of  elas- 
ticity of  cast-iron  and  wrought-iron  under  a  tensile  strain. 

The  following  example  will  illustrate  the  manner  in  which  the  proper  size  of  strength- 
ening-rings of  manholes  in  cylindrical  shells  may  be  determined :  Suppose  the  cylin- 
drical shell  of  a  boiler  to  be  £  inch  thick,  and  a  manhole  15  inches  by  12  inches  to  be 
cut  in  it,  with  the  longer  axis  in  the  circumferential  direction  of  the  boiler.  The  weak 
places  near  such  a  hole  lie  in  the  longitudinal  axis  of  the  boiler,  and  there  have  been 
removed  from  the  shell  (12  X  i  =)  6  square  inches  of  metal  in  the  line  of  this  axis. 
To  make  this  part  of  the  shell  as  strong  as  the  longitudinal  joint  of  the  shell  the  quan- 
tity of  metal  added  by  the  ring  surrounding  the  manhole  should  be  equal  to  about  65 
per  cent,  of  the  metal  cut  away,  and,  consequently,  the  cross-section  of  the  ring  at 

each  end  of  the  hole  should  be  (-  X  °'65  =  \  1.95  square  inches.     Making  the  ring  f 

inch  thick,  its  least  width  should  be  3f  inches,  if  f  inch  is  allowed  for  the  rivet-holes. 

In  English  and  French  boilers  the  strengthening-rings  around  manholes  are  often 
made  of  angle-iron,  being  in  such  a  case  riveted  to  the  outside  of  the  boiler.  This  has 
the  advantage  that  the  largest  amount  of  metal  is  concentrated  where  the  strain  on  the 
plate  is  most  severe,  and  rupture  would  commence,  and  the  greatest  stiffness  is  required 
—viz.,  at  the  edge  of  the  hole.  On  the  boiler  represented  on  Plate  XY.  the  rings  around 
the  manholes  on  the  ends  of  the  boiler  are  made  of  angle-iron  3"  X  3"  X  f. 

The  manhole-plates  are  usually  made  of  cast-iron,  the  larger  sizes  being  about  li 
inches  or  1J  inches  thick.  They  have  generally  a  dished  form,  the  convex  side  being  in- 
side the  boiler — this  form  being  best  calculated  to  resist  the  strains  on  the  plates  with- 
out buckling.  They  are  secured  to  the  boiler  by  one  or  two  wrought-iron  bolts  passing 
through  cross-bars  which  straddle  the  hole  outside  the  boiler.  These  cross-bars  are  now 
also  generally  made  of  wrought-iron.  The  bolts  are  generally  secured  permanently  to 
the  plate  by  a  countersunk  riveted  head.  Large  plates  are  provided  with  a  wrought- 
iron  handle  screwed  into  a  boss  in  the  centre  of  the  plate.  The  plate,  bolts,  and 
cross-bars  must  be  made  sufficiently  strong  and  stiff  to  bear  with  safety  and  without 
springing  the  great  strains  thrown  upon  them  in  screwing  up  the  plate.  The  bolts  are 


330 


STEAM  BOILERS. 


CHAP.  XV. 


made  with  a  coarse  thread,  and  square  nuts  should  be  used,  because  the  corners  of 
hexagonal  nuts  are  liable  to  become  rounded  when  the  wrench  does  not  fit  well. 

Instead  of  fitting  the  flange  of  a  manhole-plate  directly  to  the  cylindrical  shell  of  a 
boiler,  as  in  figure  5,  Plate  XXXI.  (which  requires  very  careful  work),  the  stiffening- 
ring  inside  the  boiler  sometimes  forms  a  plane  seat  for  the  flange  of  the  plate  ;  or,  when 
the  radius  of  the  curved  surface  is  small,  a  casting  is  riveted  to  the  outside  of  the  boiler 
around  the  manhole,  having  a  flange  which  forms  a  plane  seat  for  the  plate  (see 
figure  136). 

In  order  to  reduce  the  weight  of  large  manhole-plates  they  are  sometimes  made  of 
wrought-iron.  Figure  137  represents  the  wrought-iron  manhole-cover  of  a  boiler  de- 
Fig.  137. 


signed  for  a  working  pressure  of  70  Ibs.,  built  by  Maudslay  Sons  &  Field  (England)  in 
1873.  The  dimensions  of  the  manhole  are  15  inches  X  10  inches,  and  its  shape  is  rect- 
angular with  rounded  corners.  Two  plates  f  inch  thick  are  riveted  together  with 
countersunk  rivets.  The  outer  plate  is  of  the  size  of  the  hole,  while  the  inner  plate 
is  large  enough  to  form  the  flange  1£  inches  wide.  The  bolts  are  screwed  into  the 
plate,  the  ends  being  riveted  over.  The  ring  around  the  hole  is  1  inch  thick  and  2| 
inches  wide,  secured  by  countersunk  rivets  to  the  shell,  which  is  i  inch  thick. 

Wrought-iron  plates  made  of  a  dished  form  by  pressing  them  with  a  die  of  suitable 
shape  into  a  mould  would  be  much  stiffer  than  flat  plates,  and  could  be  made  propor- 
tionately thinner. 

Figures  1  and  5,  Plate  XXXI.,  represent  the  manhole-covers  made  recently  for 
United  States  naval  boilers.  They  are  cast  of  old  composition  metal  consisting  of  88 


SEC.  7.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  331 

parts  of  copper,  10  parts  of  tin,  and  2  parts  of  zinc.  The  wrought-iron  bolts  are  secured 
in  the  plates  by  riveting  over  the  ends,  which  pass  through  accurately-drilled  holes.  A 
handle  is  cast  on  the  plate. 

7.  Steam  Stop- valves,  Dry-pipes,  and  Steam-pipes.— The  stop-valves  of 
boilers  must  be  arranged  in  such  a  manner  that  they  are  easily  accessible  and  can  be 
opened  and  closed  quickly.  Each  boiler  must  have  a  stop- valve,  bolted  directly  to  the 
shell,  to  shut  off  all  communication  between  the  boiler  and  the  steam-pipe  connected 
with  the  engines  or  the  other  boilers.  In  case  there  are  separate  steam-drams  or  super- 
heating-chambers  the  stop-valves  and  connecting  steam-pipes  must  be  arranged  in  such 
a  way  that  any  one  of  the  boilers  or  steam-chambers  may  be  shut  off  without  the  neces- 
sity of  putting  any  of  the  others  out  of  use. 

It  is  a  safe  rule  to  make  the  area  of  stop-valves  and  steam-pipes  sufficiently  large 
that  the  velocity  of  the  steam  passing  through  them  does  not  exceed  100  feet  per 
second  when  the  speed  of  the  engines  is  a  maximum. 

Figures  1  and  2,  Plate  XXXII.,  represent  the  stop-valves  of  the  boilers  of  the  U.  S.  S. 
Nipsic,  and  may  serve  to  illustrate  the  usual  construction  of  these  valves  for  United 
States  naval  boilers.  When  the  valves  are  large  the  chamber  is  made  of  cast-iron,  and  a 
valve-seat,  made  of  composition  metal,  is  fitted  in  it  and  secured  by  riveting  over  the 
lower  end.  For  smaller  valves  the  whole  chamber  is  made  of  composition.  The  valve- 
disc  is  made  of  composition  and  of  a  dished  form  to  increase  its  stiffness,  and  it  has  a 
conical  seat.  It  is  guided  by  a  central  spindle  below,  working  easily  in  a  sleeve  con- 
nected by  ribs  to  the  valve-seat.  The  wrought-iron  stem  has  a  square  screw-thread, 
which  works  in  a  corresponding  thread  cut  in  a  cross-bar  supported  by  wrought-iron 
studs  on  the  cover  of  the  valve-chamber.  The  stem  must  not  be  rigidly  attached  to  the 
valve-disc,  so  that  the  latter  does  not  turn  with  the  stem  and  seats  itself  always  ex- 
actly. In  the  valves  represented  on  Plate  XXXII.  the  stem  passes  through  the  valve- 
disc  and  its  lower  end  forms  the  guide-spindle.  In  other  cases  the  guide-spindle  is  cast 
on  the  valve-disc,  and  the  stem  has  a  collar  at  its  lower  end  which  fits  in  a  recess 
formed  in  a  projection  on  the  top  of  the  valve-disc  ;  it  is  held  in  place  by  an  annular 
nut  screwed  to  this  projection  on  the  valve-disc  and  secured  by  a  pin. 

The  stop-valve  and  steam-pipe  must  take  the  steam  from  the  highest  part  of  the 
boiler,  where  it  is  in  the  driest  state.  When  the  boiler  has  no  vertical  steam-drum  the 
stop- valve  is  generally  connected  with  a  dry-pipe,  which  draws  the  steam  evenly  from  a 
large  area  within  the  boiler,  and  separates  to  some  extent  the  water  which  is  carried 
along  with  the  steam  from  the  latter.  The  dry -pipe  extends  through  the  length  of  the 
boiler  close  to  the  top,  and  in  large  rectangular  boilers  has  several  lateral  branches.  It 


332  STEAM  BOILERS. 


CHAP.  XV. 


is  connected  at  one  end  with  the  stop- valve  chamber  by  a  tight  joint,  while  its  other  end 
is  closed.  On  the  top  it  is  perforated  by  numerous  evenly-spaced  holes  of  about  f  inch 
diameter,  or  has  narrow,  transverse  slits  cut  into  it  by  means  of  a  saw.  The  aggregate 
area  of  these  openings  should  be  at  least  double  the  area  of  the  cross-section  of  the 
pipe. 

The  dry-pipe  is  often  made  of  cast  or  wrought  iron,  but  sheet-brass  is  a  preferable 
material,  since  the  pipe  is  much  exposed  to  corrosion. 

Dry-pipes  are  frequently  omitted  because  they  make  the  interior  of  the  boiler  less 
accessible ;  in  such  cases  the  opening  in  the  shell  is  often  protected  by  deflecting-plates 
or  by  a  box  perforated  with  numerous  holes,  in  order  to  throw  off  any  water  carried  up 
by  foaming.  When  a  boiler  foams  because  the  area  of  the  stop-valve  is  too  small,  and 
it  is  not  convenient  to  fit  dry-pipes  within  the  boiler,  it  is  better  to  place  an  additional 
stop-valve  on  the  boiler  at  some  distance  from  the  original  one  than  to  enlarge  the  ex- 
isting stop-valve. 

The  steam-pipe  should  have  as  direct  a  course  and  as  few  bends  as  possible.  Ex- 
pansion-joints must  be  provided  between  rigid  attachments  of  the  pipe,  unless  there  are 
bends  which  will  allow  the  pipe  to  spring  as  it  expands  or  contracts  in  the  direction  of 
its  length. 

Copper  pipes,  tinned  inside  and  outside  and  fitted  with  composition  flanges,  are 
generally  used  for  the  steam-pipes  of  United  States  naval  boilers.  Cast-iron  pipes  are 
far  cheaper,  but  are  heavier,  and,  from  the  unyielding  nature  of  the  material,  liable  to 
break  when  the  ship  works  much  or  in  case  the  boilers  should  move  in  their  seats. 
Wrought-iron  pipes,  either  lap- welded  or  riveted,  are  used,  but  have  the  disadvantage 
of  being  speedily  attacked  by  corrosion. 

Drain-pipes  must  be  fitted  to  all  valve-chambers  and  to  all  parts  of  the  steam-pipes 
where  water  is  liable  to  accumulate. 

The  arrangement  of  the  steam-pipes  and  stop-valves  of  the  boilers  of  the  U.  S.  S. 
Nipsic  is  shown  on  Plate  XXX. 

A  stop-valve  is  bolted  to  the  outboard  end  of  each  boiler,  connected  with  a  dry -pipe 
extending  through  the  length  of  the  boiler.  These  stop-valves  (see  figure  1,  Plate 
XXXII.)  are  operated  by  means  of  a  hand-wheel  from  below.  The  stem  is  continued 
through  the  top  of  the  valve-chamber,  and  over  each  valve  a  small  hole  is  cut  in  the 
deck,  which  is  ordinarily  kept  closed  by  a  composition  cap.  This  arrangement  makes  it 
possible  to  operate  the  valves  from  the  main  deck  by  means  of  a  socket-wrench  in  case 
the  passage  at  the  back  of  the  boilers  should  be  inaccessible. 

A  copper  pipe,  6  inches  in  diameter,  No.  13  B.  W.  Gr.  thick,  tinned  inside  and  out- 


SEC.  8.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  333 

side,  is  bolted  by  means  of  composition  flanges  ff  inch  thick  to  a  nozzle  on  the  stop- 
valve,  and  connects  each  wing  boiler  with  the  nearest  horizontal  steam-drum  above  it, 
the  middle  boiler  being  similarly  connected  to  either  drum.  A  composition  casting, 
having  suitable  nozzles  for  connecting  with  the  steam-pipes,  is  bolted  to  the  bottom  of 
each  steam-drum,  and  has  at  its  lowest  point  a  nozzle,  3  inches  in  diameter,  to  which  a 
drain-pipe  is  attached  which  leads  to  a  water-trap. 

The  inboard  end  of  each  drum  is  connected  by  means  of  a  short  wrought-iron  nozzle 
with  the  superheating  steam-pipe  passing  through  the  length  of  the  uptake  at  either 
side  of  the  vessel.  These  superheating-pipes  are  of  wrought-iron,  lap-welded.  They 
are  9  inches  in  diameter,  0.344  inch  thick,  and  have  wrought-iron  flanges  1  inch  thick 
riveted  to  them.  The  nozzles  connecting  the  drums  with  the  superheating-pipes  are 
riveted  to  the  latter.  Each  superheating-pipe  is  made  in  two  lengths  ;  the  flanges  con- 
necting them  are  surrounded  by  an  iron  casing  which  protects  the  joint  from  the  heat  of 
the  uptake.  A  safety-valve  is  attached  to  the  forward  end,  and  a  stop-valve  9f  inches 
in  diameter  (see  figure  2,  Plate  XXXII.)  is  attached  to  the  after  end  of  each  superheat- 
ing-pipe. A  copper  pipe,  8£  inches  in  diameter,  No.  12  B.  W.  G.  thick,  bolted  by 
means  of  a  composition  flange  £  inch  thick  to  a  nozzle  of  the  valve-chamber,  conveys  the 
steam  from  the  boilers  to  the  engines. 

Each  forward  and  after  wing  boiler  at  either  side  of  the  vessel  is  connected  by  means 
of  a  stop-valve,  4f  inches  in  diameter  and  bolted  to  the  cylindrical  shell  of  the  boiler, 
with  a  copper  pipe  leading  over  the  top  of  the  boilers  to  the  auxiliary  pumps  and  to  the 
distiller. 

The  steam-pipes  and  stop-valves  for  the  United  States  ironclad  Miantonomoh  and 
class  are  described  in  the  specifications  of  the  boilers  of  these  vessels  in  section  10, 
chapter  vii. 

8.  Check-valves  and  Feed-pipes — A  check-valve,  consisting  of  a  disc-valve  with 
a  conical  seat,  is  placed  between  the  feed-pipe  and  the  boiler.  The  valve  is  kept  closed 
by  the  pressure  within  the  boiler  acting  on  its  upper  surface,  and  rises  with  each  stroke 
of  the  pump  as  the  water-pressure  within  the  feed-pipe,  acting  on  the  lower  surface  of  the 
valve,  exceeds  the  boiler-pressure.  A  detached  stem  with  a  square  thread  bears,  when 
it  is  screwed  down,  on  the  upper  surface  of  the  valve  and  keeps  it  closed,  and  when 
raised  regulates  the  lift  of  the  valve,  and  consequently  the  supply  of  feed- water  to  the 
boiler.  For  guiding  the  valve  it  is  provided  below  its  seat  with  three  or  four  wings, 
or  with  a  central  spindle  working  in  a  sleeve,  and  above  by  a  spindle  working  in  a 
socket  in  the  enlarged  end  of  the  detached  stem. 

When  check-valves  have  much   lift  the  hammering  action  of  the  valve   causes 


334  STEAM  BOILERS.  CHAP.  XV. 

the  rapid  destruction  of  the  valve  and  seat,  so  far  as  tightness  is  concerned,  especially 
with  a  quick-acting  pump.  The  lift  of  a  check-valve  should  not  exceed  ordinarily  £ 
inch ;  and  the  area  of  the  valve  should  be  such  that  with  this  lift  the  rate  of  flow 
of  the  feed-water  through  the  valve-opening  does  not  exceed  600  feet  per  minute. 

Since  much  trouble  is  caused  by  check- valves  leaking  or  not  closing  properly  when 
foreign  matter  lodges  between  the  valve  and  its  seat,  a  stop- valve  is  frequently  placed 
between  the  check- valve  and  the  boiler,  which  permits  the  communication  between  the 
boiler  and  check- valve  to  be  cut  off  for  the  purpose  of  examining  and  cleaning  the 
latter.  This  stop-valve  is  also  used  for  regulating  the  supply  of  feed-water  to  the 
boiler. 

In  such  a  case  the  upper  spindle  of  the  check- valve  is  sometimes  continued  through 
the  chest-cover,  and  carries  a  weight  on  its  top  which  is  sufficiently  heavy  to  overcome 
the  friction  of  the  stem  in  the  stuffing-box  and  ensures  the  prompt  seating  of  the  valve 
after  each  stroke  of  the  pump. 

Plug-cocks  are  preferred  by  many  engineers  to  screw  stop-valves  on  feed-pipes,  be- 
cause the  latter  may  be  prevented  from  shutting  by  some  solid  matter  getting  under  the 
valve-disc  ;  but  cocks  of  large  dimensions  are  often  very  difficult  to  turn,  and  a  feed- 
cock  which  cannot  be  opened  causes  much  greater  inconvenience  than  a  feed-valve 
which  cannot  be  shut  tight. 

Figure  3,  Plate  XXXII.,  represents  the  feed  and  check  valves  of  the  boilers  of  the 
U.  S.  S.  Nipsic.  A  stop- valve  is  placed  between  the  boiler  and  the  check-valve,  and  a 
like  stop-valve  is  placed  between  the  check- valve  and  the  feed-pipe.  These  three  valves 
have  all  an  opening  2|  inches  in  diameter,  and  are  contained  in  a  single  casting  made 
of  composition  metal.  The  stem  of  the  stop-valves  is  made  of  steel.  The  upper  guide- 
sleeve  of  the  check-valve  is  cast  on  the  cover  of  the  chamber,  and  the  cover  is  held 
down  by  a  single  bolt  passing  through  a  wrought-iron  bail. 

The  check-valve  chamber  is  bolted  directly  to  the  shell  of  the  boiler  at  such  a  place 
where  it  is  most  conveniently  situated  for  controlling  the  feed-supply.  It  is  generally 
placed  on  or  near  the  front  of  the  boiler  at  about  the  height  of  the  furnace-crown,  and 
discharges  the  water  directly  into  the  boiler.  It  is  objected  to  this  arrangement  that  the 
comparatively  cold  feed-water  causes  injury  by  impinging  directly  against  the  most 
highly  heated  part  of  the  boiler.  On  this  account  an  internal  pipe  is  sometimes  pro- 
vided which  leads  downward,  discharging  the  feed-water  near  the  bottom  of  the  boiler. 
In  other  instances  this  internal  pipe  leads  upward,  discharging  the  water  near  the 
smoke-connection,  where  the  temperature  of  the  gases  is  least ;  with  the  latter  arrange- 
ment the  cool  feed-water,  sinking  by  gravity,  promotes  also  the  circulation  of  the  water 


SEC.  9.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  335 

in  the  boiler.  In  some  cases  the  internal  pipe,  continued  horizontally  across  the  smoke- 
box  end  of  the  tubes,  has  been  provided  with  numerous  small  openings  throughout  its 
length,  through  which  the  feed- water  is  distributed  over  a  wide  space  instead  of  being 
discharged  in  a  mass  at  one  point. 

The  feed-pipes  for  United  States  naval  boilers  are  generally  either  cast  of  composi- 
tion metal  or  are  made  of  drawn-brass  tubes  connected  by  composition  flanges  and 
heavily  tinned  on  the  inside.  Copper  pipes  have  been  abandoned  on  account  of  the 
galvanic  action  produced  in  the  boiler  by  the  small  particles  of  copper  abraded  and 
carried  along  by  the  feed-water.  Cast-iron  pipes  are  heavy  and  become  soon  perfo- 
rated with  small  holes. 

The  feed-pipes  must  be  made  with  as  few  bends  as  possible ;  when  they  are  long 
they  must  be  provided  with  slip-joints.  The  feed-pipes  must  be  placed  where  they 
are  easily  examined  and  repaired. 

The  usual  arrangement  of  the  feed-pipes  in  United  States  naval  vessels  may  be 
seen  on  Plate  XXX.,  illustrating  the  boilers  of  the  U.  S.  S.  Nipsic.  A  feed-pipe,  made 
of  composition  and  having  3  inches  internal  diameter,  runs  along  the  front  of  the  boilers 
at  either  side  of  the  vessel  below  the  fire-room  floor ;  and  it  is  connected  by  vertical 
branch-pipes,  having  an  internal  diameter  of  2£  inches,  with  the  check-valve  chamber  of 
each  boiler. 

See  section  10,  chapter  vii.,  for  the  specifications  of  the  feed-pipes  and  check- valves 
of  the  boilers  of  the  United  States  iron-clad  Miantonomoh  and  class. 

9.  Blow-valves  and  Pipes. — While  marine  boilers  were  worked  with  very  low 
steam-pressure,  pumps  were  used  to  withdraw  continuously  a  certain  quantity  of  the 
concentrated  water  from  the  boiler,  so  as  to  maintain  the  saturation  within  the  boiler 
at  a  given  point.  But  these  brine-pumps  have  gone  out  of  use,  and  the  water  is 
blown  from  the  boiler  overboard  directly  by  the  steam-pressure,  the  quantity  thus 
blown  out  being  regulated  by  the  opening  of  the  blow-valves  provided  for  the  purpose. 

The  blow-valves  of  United  States  naval  boilers  are  generally  disc-valves  with  a  coni- 
cal seat,  operated  by  means  of  a  screw-thread  cut  on  the  stem  of  the  valve ;  the 
valves  and  valve-chambers  are  made  of  composition  metal,  and  are  similar  in  construc- 
tion to  the  stop  and  feed  valves  represented  on  Plate  XXXII.  It  is  urged  against  the 
iise  of  disc-valves  that  small  chips,  pieces  of  incrustation,  or  other  solid  matter  are 
liable  to  lodge  on  the  seat  of  such  valves  and  prevent  their  closing  tight  when  to  all 
outward  appearance  they  may  seem  quite  shut.  On  this  account  cocks  are  preferred 
by  many  engineers  for  blow-valves. 

The  principal  drawback  to  the  use  of  large  cocks  is  their  liability  to  stick  fast  in 


336  STEAM  BOILERS.  CHAP.  XV. 

consequence  of  corrosion  or  incrustation,  of  unequal  expansion  of  the  plug  and  shell, 
or  of  other  causes  producing  excessive  friction.  The  tendency  to  stick  fast  is  greatly 
aggravated  when  the  shell  is  made  of  cast-iron  and  the  plug  of  brass ;  both  should 
be  made  of  composition  metal,  not  too  soft.  "For  pressures  of  20  or  30  Ibs.  a  taper  of 
one  in  four  is  found  to  work  well,  but  for  pressures  of  90  or  100  Ibs.  a  taper  of  one  in 
six  is  necessary  to  ensure  tightness."  ( Wilson.} 

The  regulations  of  the  Board  of  Trade  (English)  prescribe  that- 
'll! blow-off  cocks  and  sea-connections  are  to  be  fitted  with  a  guard  over  the 
plug,  with  a  feather- way  in  the  same,  and  a  key  on  the  spanner,  so  that  the  spanner 
cannot  be  taken  out  unless  the  plug  or  cock  is  closed.  One  cock  is  to  be  fitted  to  the 
boiler,  and  another  cock  on  the  skin  of  the  ship  or  on  the  side  of  the  Kingston 
valve." 

The  chamber  of  the  blow-valve  is  bolted  directly  to  the  shell  of  the  boiler  in  a 
convenient  position  on  or  near  the  front  of  the  boiler. 

The  bottom  blow-valve  is  used,  while  the  boiler  is  in  operation,  to  remove  the  dirt  and 
sediment  which  collects  in  the  bottom  of  the  boiler  by  discharging  a  limited  quantity 
of  water  at  intervals,  and  to  fill  the  boiler  with  water  from  the  sea  before  starting 
the  fires,  and  to  empty  the  boiler  after  hauling  the  fires.  The  blow-valve  takes  the 
water  from  the  bottom  of  the  boiler  through  an  internal  pipe  secured  with  a  tight 
joint  to  the  shell  of  the  boiler.  The  bottom  blow-valve  is  generally  made  of  the  same 
size  as  the  feed-valve,  so  that  the  boiler  may  be  filled  and  emptied  quickly. 

The  surface  blow-valve  is  generally  made  about  one-half  as  large  as  the  feed- valve. 
It  is  used  to  remove  the  scum  and  other  impurities  floating  near  the  surface  of  the 
water.  The  valve  is  connected  with  a  system  of  perforated  pipes  extending  through 
the  boiler  a  short  distance  below  the  water-line,  or  with  one  or  several  perforated 
boxes  or  strainers  in  which  the  water,  being  undisturbed  by  ebullition,  deposits  the 
solid  particles  held  in  suspension. 

The  arrangement  of  the  blow- valves  and  pipes  of  the  boilers  of  the  TJ.  S.  S.  Nipsic 
is  shown  on  Plate  XXX.  The  bottom  blow- valves  of  the  several  boilers  on  each  side 
of  the  vessel  are  connected  by  means  of  composition  branch-pipes,  2£  inches  in  internal 
diameter,  with  the  main  blow-pipe  leading  along  the  front  of  the  boilers  to  the  Kingston 
valve  in  the  bottom  of  the  vessel.  The  main  blow-pipes  are  made  of  seamless  drawn 
brass  tubes,  connected  by  flanges,  and  are  provided  with  a  slip-joint.  The  pipes  of  the 
surface  blow-valves  are  connected  with  a  stop-valve  on  the  side  of  the  vessel  a  short 
distance  below  the  water-line  ;  and  a  branch-pipe  connects  the  surface  blow-pipe  also 
with  the  bottom  blow-pipe. 


SEC.  10.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  337 

The  blow-pipes  are  frequently  exposed  to  violent  shocks  and  jars  when  they  are  dis- 
charging the  hot  water  into  the  sea.  On  this  account  bends  must  be  avoided  as  much 
as  possible  and  must  be  made  with  easy  curves,  and  the  pipes  must  be  made  of  a  tough 
material.  The  use  of  cast-iron  is  to  be  condemned.  Brazed  copper  pipes  are  liable  to 
split.  Cast  composition  or  seamless  drawn  brass  pipes  are  nowadays  generally  used  for 
the  blow-pipes  of  United  States  naval  boilers.  (See  "  Specifications  for  Boilers  of 
United  States  Ironclad  MiantonomoJi  and  Class,'''  section  10,  chapter  vii.) 

1O.  Instruments  and  Attachments  for  Measuring  and  Indicating  the 
Height  and  the  Density  of  the  Water,  and  the  Pressure  and  Temperature 
of  the  Steam. 

Water-gauges.—  The  rules  and  regulations  of  the  Supervising  Inspectors  of 
Steam-vessels  provide  that  "all  steamers  having  one  or  more  boilers  shall  have  three 
suitable  gauge-cocks  in  each  boiler  ;  those  having  three  or  more  boilers  in  battery  shall 
have  three  in  each  outside  boiler  and  two  in  each  remaining  boiler  in  the  battery  ;  and 
the  middle  gauge-cocks  in  all  boilers  shall  not  be  less  than  4  inches  above  the  top  of  the 
flues,  tubes,  or  crown  of  the  fire-box." 

United  States  naval  boilers  are  fitted  with  three  or  four  water-gauge  cocks,  placed 
from  4  to  6  inches  apart,  the  lowest  gauge-cock  being  placed  on  a  line  with  the  top  of 
the  back-connections.  Either  screw-valves  with  conical  seats  or  plug-cocks  are  used  for 
water-gauges.  To  keep  their  opening  clear  of  any  solid  matter  the  valves  are  provided 
with  feathers  projecting  beyond  the  opening  of  the  valve-cham-  Fig.  138. 

ber  (see  Plate  XXXIII.)  Provision  is  made  to  clear  plug-cocks 
by  means  of  a  wire,  by  forming  a  straight  passage  through  them, 
which  is  ordinarily  kept  closed  by  a  screw-plug  at  the  front  end 
(see  figure  138).  The  gauge-cocks  discharge  the  steam  and  water 
into  a  copper  drip-pan  provided  with  a  drain-pipe  which  leads 
down  into  the  bilge  of  the  vessel  or  to  a  water-trap. 

In  addition  to  the  gauge-cocks  boilers  are  generally  provided  with  water-gauge 
glasses,  consisting  of  a  glass  tube  from  12  to  18  inches  long,  the  top  and  bottom  of 
which  communicate  by  means  of  suitable  fittings  with  the  steam  and  water  spaces  re- 
spectively, so  that  the  water  within  the  glass  stands  at  the  same  level  as  the  water 
within  the  boiler.  Pipes  lead  from  the  top  and  bottom  of  the  gauge  well  up  into  the 
steam-space  and  down  into  the  water-space  respectively,  so  that  the  indications  of  the 
water-level  in  the  glass  are  not  affected  by  violent  ebullitions  and  foaming.  These 
pipes  should  not  be  less  than  one  inch  in  diameter,  so  as  not  to  be  clogged  easily  by 
pieces  of  loose  scale  or  impurities  in  the  water. 


338  STEAM  BOILERS.  CHAP.  XV. 

Gauge-glasses  must  be  made  of  a  white,  transparent  glass  without  bubbles  or  other 
defects  which  would  impair  their  strength,  and  must  be  carefully  annealed.  Gauge- 
glasses  have  been  introduced  of  late  in  which  the  side  of  the  glass  turned  toward  the 
boiler  is  covered  with  a  white  enamel,  while  the  other  half  is  left  transparent ;  on  the 
white  background  the  line  of  the  water-level  is  more  plainly  seen. 

At  the  top  and  bottom  the  glass  fits  in  a  stuffing-box  with  a  screw-gland,  and  is 
packed  with  soft  rubber  or  cotton-wick.  Cocks  or  screw-valves  are  provided  for  shut- 
ting off  the  communication  between  the  gauge  and  the  boiler  at  the  top  and  bottom,  and 
for  opening  a  passage  between  the  gauge-glass  and  the  drain-pipe.  All  the  passages  of 
the  gauge  must  be  of  such  size  and  form  that  they  are  not  clogged  easily  by  dirt,  and 
so  arranged  that  they  can  be  cleared  while  the  boiler  is  in  operation. 

The  water-gauge  cocks  and  glasses  are  either  placed  directly  on  the  front  of  the 
boiler  or  they  are  attached  to  a  tube  made  of  composition  or  cast-iron  and  having  an 
internal  diameter  of  2J  or  3  inches.  This  tube  is  placed  close  to  the  boiler,  with  its 
upper  and  lower  ends  communicating  with  the  steam  and  water  spaces  as  described 
above. 

Plate  XXXIII.  illustrates  the  type  of  water-gauge  recently  constructed  for  the  boil- 
ers of  the  U.  S.  S.  Nipsic  and  other  United  States  naval  vessels.  A  glass  gauge  and 
four  gauge-cocks  are  attached  to  a  composition  casting,  the  general  outline  of  which  is 
cylindrical,  so  that  its  whole  exterior  can  be  finished  by  turning.  This  casting  contains 
several  small  compartments  and  passages  and  one  large  chamber  extending  through 
the  length  of  the  casting  and  connected  at  the  top  and  bottom  with  the  boiler  by  means 
of  composition  pipes  1J  inches  in  internal  diameter.  The  communication  between  these 
pipes  and  the  boiler  may  be  shut  off  by  means  of  plug-cocks  placed  on  the  shell  of  the 
boiler  (see  Plate  XXX.)  Four  gauge-cocks,  consisting  of  screw-valves  with  conical 
seats,  and  placed  6  inches  apart,  are  screwed  into  a  recessed  plane  face  of  the  casting, 
and  communicate  directly  with  the  large  chamber.  The  cylindrical  shell  of  the  casting 
forms  a  shield  enclosing  the  discharge-nozzles  of  the  gauge-cocks  and  leading  the 
steam  and  water  blown  out  to  a  waste-passage  at  the  bottom  of  the  casting.  A  gauge- 
glass,  having  an  external  diameter  of  f  inch  and  an  exposed  length  of  19  inches,  enters 
at  the  top  and  bottom  into  small  separate  compartments,  which  communicate  by  means 
of  screw- valves  with  the  large  chamber  and  with  a  waste-passage,  to  the  lower  end  of 
which  a  copper  drain-pipe  f  inch  in  diameter  is  attached.  Behind  the  gauge-glass  a 
lamp  is  placed  from  the  side,  which  can  be  moved  up  or  down  and  clamped  in  any 
position. 

These  gauges  are  made  right  and  left.     All  the  fittings  are  of  composition.     The 


SEC.  10.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  339 

handles  of  the  gauge-cocks  are  all  placed  at  the  same  angle  when  the  cocks  are 
shut. 

Some  years  ago  percussion  water-gauges  were  frequently  used  on  United  States 
naval  boilers  in  addition  to  the  gauge  cocks  and  glasses.  They  are  especially  intended 
to  indicate  the  height  of  solid  water  when  the  boilers  foam  badly.  They  consist  of  a 
cylinder,  made  of  composition  metal,  about  4  inches  in  diameter  and  about  20  inches 
long,  connected  at  the  top  and  bottom  by  means  of  pipes  with  the  steam  and  water 
spaces  of  the  boiler,  and  placed  at  about  the  same  height  on  the  front  of  the  boiler  as 
the  water-gauge  cocks  and  glass.  This  cylinder  contains  an  easily-fitting  piston,  with 
a  rod  passing  through  a  stuffing-box  on  the  top,  to  which  a  handle  is  attached  which 
leads  downwards  and  carries  a  pointer  at  the  same  level  as  the  piston.  The  latter 
having  been  raised  clear  of  the  water,  it  is  easy  to  feel  when  it  strikes  the  water  on 
being  pulled  down  suddenly,  and  the  position  of  the  pointer  relatively  to  rings  formed 
on  the  outside  of  the  cylinder  shows  the  height  of  the  water  in  the  boiler. 

In  another  class  of  devices  a  float  indicates  the  height  of  the  water  in  the  boiler. 
This  float  is  formed  frequently  by  a  large  hollow  sphere  which  floats  in  an  upright 
cylindrical  vessel  in  which  the  water  stands  at  the  same  level  as  in  the  boiler.  The 
position  of  the  water-level  is  indicated  by  a  pointer,  which  is  moved  by  a  rod  attached 
to  the  float. 

In  the  Belleville  boiler  such  a  float  is  used  to  regulate  the  quantity  of  feed-water 
admitted  by  adjusting  the  opening  of  the  feed-valve.  In  other  cases  the  float  admits 
steam  to  an  alarm-whistle  when  the  water  falls  below  a  certain  height. 

Floats  are,  however,  seldom  used  on  marine  boilers ;  they  are  more  applicable  to 
stationary  and  steamboat  boilers  which  are  always  fed  with  fresh  water,  and  where 
their  indications  are  not  affected  by  violent  motions  of  the  vessel. 

Fusible  Plugs. — Another  safeguard  against  the  dangers  arising  from  low  water  in 
the  boiler  is  the  fusible  plug  which  closes  a  small  hole  in  the  water-heating  surface 
of  the  boiler  at  a  height  below  which  the  water  cannot  be  allowed  to  fall  without  immi- 
nent danger.  The  plug  is  made  of  some  metal  or  alloy  which  will  melt  before  the 
iron  is  overheated  to  a  dangerous  degree.  The  discharge  of  steam  through  the  hole 
thus  formed  gives  warning  of  the  danger  and  at  the  same  time  relieves  the  pressure 
within  the  boiler  and  retards  the  combustion. 

The  rules  and  regulations  of  the  Supervising  Inspectors  of  Steam-vessels  re- 
quire that  all  fire-box  boilers  shall  have  one  plug  of  Banca  tin  1  inch  in  diameter 
inserted  in  the  crown  of  the  back-connection.  These  fusible  plugs  are  never  used  in 
United  States  naval  boilers. 


340  STEAM  BOILERS.  CHAP.  XV. 

Salinometer-pots. — All  boilers  of  United  States  naval  vessels  are  provided  with  per- 
manently-attached salinometer-pots  for  testing  the  density  of  the  water  in  the  boiler. 
The  water-pipes  through  which  the  pots  communicate  with  the  boilers,  as  well  as  the 
drain-pipes,  are  made  of  copper  or  brass  about  £  inch  in  diameter,  and  are  connected 
by  means  of  screw-couplings,  so  as  to  be  easily  detached  for  cleaning.  Stop-cocks  are 
provided  to  open  and  shut  off  communication  between  the  pipe  and  the  pots  and  boil- 
ers. The  water-pipe  must  be  connected  to  the  boiler  at  some  place  above  the  furnace- 
crowns  where  the  temperature  of  the  water  is  equal  to  that  of  the  steam,  and  not  in  the 
vicinity  of  the  feed- valve. 

The  object  sought  to  be  obtained  in  the  construction  of  salinometer-pots  is  to  main- 
tain in  an  open  vessel  a  constant  flow  of  the  water  drawn  from  the  boiler  while  testing 
its  density,  and  to  reduce  this  water  to  a  fixed  temperature  below  the  boiling-point 
under  atmospheric  pressure,  so  as  to  avoid  ebullition  and  the  formation  of  clouds  of 
vapor. 

Long's  salinometer-pot,  which  has  been  in  use  on  United  States  naval  boilers  for 
many  years,  consists  of  two  brass  cylindrical  vessels  placed  side  by  side  and  communi- 
cating at  the  bottom.  The  water  enters  one  of  these  vessels,  which  is  kept  closed  by  a 
cover  perforated  with  a  few  small  holes  for  the  escape  of  steam,  through  a  central  pipe 
closed  at  the  top  and  perforated  near  its  upper  end.  The  rate  of  flow  of  the  water  from 
the  boiler  is  regulated  by  a  stop-cock.  The  water  rises  simultaneously  in  the  two  ves- 
sels. A  central  tube  reaching  nearly  to  the  top  of  the  second  vessel,  which  is  kept 
open,  serves  as  an  overflow.  This  overflow-pipe  passes  through  the  bottom  of  the  pot 
and  is  coupled  to  a  drain-pipe ;  another  drain-pipe  communicates  with  the  bottom  of 
the  vessels  to  draw  off  the  water  from  them.  The  hydrometer  is  placed  in  the  open 
vessel,  which  is  provided  at  the  side  with  clamps  for  holding  a  thermometer  which  indi- 
cates the  temperature  of  the  water  during  the  test. 

fitTiian's  salinometer-pots  have  been  used  on  several  United  States  naval  boilers 
since  the  introduction  of  higher  steam-pressures.  The  hot  water  drawn  from  the  boiler 
passes,  before  it  enters  the  open  vessel,  through  a  coiled  pipe  immersed  in  a  stream  of 
cold  water.  By  regulating  the  flow  of  the  cooling  water  the  temperature  of  the  water 
which  is  to  be  tested  can  be  regulated  quickly  and  exactly. 

Steam-gauges. — Each  boiler  must  be  connected  with  a  separate  steam-gauge,  which 
must  communicate  directly  with  the  boiler  and  not  with  the  steam-pipe,  so  that  the  clos- 
ing of  a  stop-valve  does  not  put  the  gauge  out  of  use.  The  gauge  is  located  at  a  conve- 
nient place  in  the  fire-room,  and  is  connected  with  the  top  of  the  boiler  by  a  copper  or 
brass  pipe  about  £  inch  in  diameter,  to  which  a  downward  ciirve  is  given  close  to  the 


SBC.  11.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  341 

gauge,  so  that  the  water  accumulating  at  this  point  prevents  the  hot  steam  from  coming 
in  contact  with  the  spring  of  the  gauge.  Plug-cocks  are  placed  on  the  boiler  and  on  the 
gauge,  and  the  pipe  is  connected  to  them  by  screw-couplings.  It  is  advisable  to  use  a 
soft  lead  washer  as  a  packing  in  the  coupling,  as  rubber  is  apt  to  swell  and  be  squeezed 
out  till  it  closes  the  opening  of  the  small  pipe. 

United  States  naval  vessels  have  generally,  in  addition  to  the  spring-gauges  attached 
to  each  boiler,  one  standard  mercurial  gauge,  which  is  connected  with  the  main  steam- 
pipe  of  the  boilers. 

Thermometers. — All  separate  superheating-chambers  should  be  fitted  with  thermo- 
meters, especially  when  the  steam  is  superheated  to  a  high  degree.  The  thermometer 
must  be  immersed  in  the  steam  as  far  as  possible,  leaving  only  such  a  length  of  the  stem 
exposed  as  is  necessary  to  read  the  instrument.  The  part  of  the  instrument  which  is 
immersed  in  the  steam  is  surrounded  by  a  perforated  pipe  ;  the  projecting  stem  is  pro- 
tected by  a  shield-plate,  or  by  a  brass  case  fitted  with  a  sliding-plate. 

11.  Safety-valves. — Each  boiler  must  be  provided  with  a  safety-valve,  arranged  in 
such  a  manner  that  the  communication  between  the  valve  and  the  boiler  cannot  be  shut 
off.  A  safety-valve  must  also  be  provided  for  each  separate  superheating-chamber  and 
feed- water  heater.  The  safety-valve  should  be  placed  on  the  top  of  the  boiler  or  be  con- 
nected by  an  internal  pipe  with  the  highest  part  of  the  steam-space. 

Safety-valves  must  be  so  arranged  that  they  may  be  opened  by  hand  in  order  to 
relieve  the  boiler  of  steam-pressure  at  any  time  and  to  try  whether  the  valve  moves 
freely  in  its  seat.  The  rules  of  Government  inspectors  require  that,  in  addition,  each 
boiler  shall  carry  a  lock-up  safety-valve  of  sufficient  size,  which,  being  set  to  blow  off  at 
the  pressure  allowed,  is  entirely  beyond  the  control  of  the  persons  manipulating  the 
machinery. 

Safety-valves  are  weighted  by  applying  the  load  to  them  either  directly  or  by  means 
of  a  lever.  Springs  are  used  almost  universally  instead  of  weights  for  directly-loaded 
valves  on  marine  and  locomotive  boilers  ;  they  are  also  frequently  used  for  lever  safety- 
valves.  Spring-loaded  valves  come  more  and  more  into  use  in  sea-going  steamers 
where  steam  of  high  pressure  is  used,  on  account  of  the  difficulties  incident  to  the  use  of 
heavy  weights  in  consequence  of  the  violent  motions  of  vessels  in  rough  weather.  When 
the  lever  of  safety-valves  is  loaded  by  dead  weights  it  is  placed  in  the  fore-and-aft 
direction  of  the  vessel. 

In  a  spring-loaded  valve  the  tension  or  compression  of  the  spring  increases  with  the 
lift  of  the  valve,  while  the  weight  of  a  dead  load  is  the  same  for  every  lift.  But  with  a 
properly-proportioned,  directly-loaded  valve  the  increase  of  resistance  of  the  compressed 


342  STEAM  BOILERS.  CHAP.  XV. 

or  extended  spring  is  trifling.  When  the  spring  acts  on  a  lever  some  compensating 
arrangement  should  be  adopted  to  counteract  the  effect  of  the  increased  resistance. 

A  safety-valve  acting  automatically  must  fulfil  the  following  essential  conditions— 
viz. : 

It  must  be  capable  of  discharging  at  a  given  pressure  the  greatest  weight  of  steam 
which  the  boiler  is  capable  of  generating  in  a  unit  of  time. 

It  must  not  allow  the  pressure  within  the  boiler  to  rise  above  a  fixed  limit,  and  it 
must  close  quickly  when  the  pressure  falls  below  that  at  which  the  valve  is  set  to  open. 

It  must  be  reliable  in  its  action  under  continued  use  ;  it  must  be  simple  in  its  con- 
struction and  easily  adjusted  and  managed. 

The  size  of  the  valve  must  be  proportioned  to  the  greatest  weight  of  steam  which  may 
be  generated  in  a  unit  of  time.  Rules  which  determine  the  size  of  safety-valves  by  the 
dimensions  of  the  grate  or  heating  surface,  or  by  the  weight  of  coal  consumed  in  a  unit 
of  time,  are  based  on  the  supposition  that  under  the  given  conditions  a  fixed  rate  of 
evaporation  obtains,  and  apply  consequently  only  to  special  classes  of  boilers.  A  gene- 
ral rule  must  determine  the  area  of  the  valve  by  the  weight  of  steam  to  be  discharged 
in  a  unit  of  time  and  by  the  pressure  at  which  it  is  to  be  discharged. 

The  weight  of  steam,  in  pounds,  discharged  into  the  atmosphere  per  second  through 
an  orifice  having  an  area  of  1  square  inch,  is  approximately  equal  to  the  absolute  pres- 
sure of  steam  in  pounds  per  square  inch  divided  by  70  when  the  steam -pressure  is  equal 
to  or  greater  than  25  pounds  per  square  inch  above  zero.  (Rarikine,  '  Manual  of  the 
Steam-engine. ' ) 

The  effective  opening  of  a  safety-valve  lifting  automatically  is  very  small  relatively 
to  the  area  of  its  disc,  because  the  lift  of  the  valve  is  always  small.  With  the  ordinary 
disc-valve  a  greater  lift  than  -^  inch  should  not  be  counted  upon.  This  small  lift  is  due 
to  the  rapid  diminution  of  the  force  exerted  by  the  steam-pressure  on  the  valve  as  it 
rises  from  its  seat.  Various  methods  have  been  tried  of  increasing  the  lift  of  the  valve 
by  making  the  escaping  steam  impinge  on  a  lip  turned  down  around  the  rim  of  the 
valve,  or  by  otherwise  obstructing  the  passage  of  the  escaping  steam  (see  figure  3,  Plate 
XXXIV.,  representing  Ashcroft's  safety-valve).  But,  in  general,  such  arrangements 
tend  also  to  produce  an  excess  of  pressure  within  the  boiler  over  the  pressure  at 
which  the  valve  begins  to  lift,  or  to  make  the  action  of  the  valve  irregular  or  inter- 
mittent. 

A  further  diminution  of  the  effective  opening  of  valves  is  due  to  the  conical  form 
ordinarily  given  to  the  seat.  „ 

The  safety-valve  must  discharge  the  steam,  when  the  evaporation  is  a  maximum,  so 


SEC.  11.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  343 

rapidly  tha,t  the  greatest  increase  of  pressure  within  the  boiler  does  not  exceed  10  or  12 
per  cent,  of  the  pressure  at  which  the  valve  begins  to  lift. 

When  the  diameter  has  to  exceed  5  inches  in  order  to  get  sufficient  area,  it  is  better 
to  increase  the  number  than  the  size  of  the  valves. 

Thurston   proposes    the  following  formula  for   determining  the  area   of  safety- 
valves  : 

0.5  w 


A  = 


IO 


when    A  =  area  of  safety-valve  in  square  inches  ; 

p  —  pressure  of  steam  in  pounds  per  square  inch  above  the  atmosphere ; 
w  =  weight  of  water,  in  pounds,  evaporated  per  hour  as  a  maximum. 

Rankine  proposed  the  following  rule  for  determining  the  area  of  safety-valves : 
Multiply  the  number  of  pounds  of  water  evaporated  per  hour  by  0.006  ;  tJie  product 
will  be  the  area  of  the  valve  in  inches. 

The  rules  of  the  United  States  Supervising  Inspectors  of  Steam-vessels,  of  the  Board 
of  Trade  (English),  and  of  Lloyd's  Register  require  that  the  safety-valves  of  marine 
boilers  shall  have  an  area  of  not  less  than  half  a  square  inch  to  each  square  foot  of 
grate-surface  when  the  ordinary  safety-valve  is  employed.  But  when  a  safety-valve  of 
an  approved  pattern  is  used  which  gives  a  greater  lift  than  the  common  safety-valve 
the  size  of  the  valve  may  be  diminished. 

In  the  report  on  safety-valve  tests,  made  in  1875  at  the  United  States  Navy- 
Yard,  Washington,  D.  C.,  by  a  special  committee  of  the  Board  of  Supervising  Inspec- 
tors of  Steam-vessels,  it  is  stated  that  an  ordinary  disc-valve  with  a  bevelled  seat, 
having  an  area  of  ten  square  inches,  will  discharge  two  thousand  pounds  of  steam  in  an 
hour  at  all  pressures  from  20  to  100  Ibs.  per  square  inch.  The  following  rule  for  deter- 
mining the  size  of  safety-valves  is  deduced  from  these  experiments  : 

Multiply  the  weight  of  water  in  pounds  evaporated  in  one  hour  by  0.005  ;  the  re- 
sult is  the  area  of  the  valve-disc  in  square  inches. 

It  is  likewise  recommended  that  the  area  of  safety-valves  should  not  exceed  ten 
square  inches,  and  that  several  valves  be  employed  when  a  larger  area  is  required  for  a 
boiler. 

Numerous  forms  of  safety-valves  and  arrangements  for  loading  them  have  been  de- 
vised. Annular  valves  and  double  poppet-valves  have  been  used  for  the  purpose  of 
obtaining  a  large  area  of  opening  with  a  given  lift.  In  other  cases  an  auxiliary  valve 
or  piston  has  been  used  in  combination  with  the  safety-valve,  with  a  view  to  increasing 


r  THE 
UNIVERSITY 

OF 


34.4  STEAM  BOILERS.  CHAP.  XV. 

the  lift  of  the  valve  and  ensuring  its  prompt  seating  when  the  pressure  falls  below  the 
point  for  which  the  valve  is  set.  But,  generally  speaking,  the  ordinary  disc- valve  is 
not  only  the  simplest  in  construction,  but  most  reliable  in  its  action  and  least  liable  to 
derangement. 

Disc- valves  are  made  either  with  a  conical  or  with  a  flat-faced  seat.  It  is  claimed  for 
the  latter  that  they  are  less  liable  to  stick  and  that  they  present  a  larger  opening  with  the 
same  lift  than  the  former.  On  the  other  hand,  it  is  objected  that  it  is  more  difficult  to 
keep  them  tight,  and  that  the  steam  escapes  with  greater  difficulty  through  their  open- 
ing, since  it  has  to  make  two  abrupt  changes  in  direction.  When  a  wide  bearing-surface 
is  given  to  flat-faced  valves  they  are  apt  to  have  a  trembling,  vibratory  motion  when  they 
are  discharging  steam. 

Conical  valves  are  most  usually  employed,  the  bevel  of  their  seat  forming  an  angle 
of  45°.  With  a  narrow  face  the  valve  is  more  easily  kept  tight  and  the  steam  escapes 
with  greater  ease  than  with  a  wide  face  ;  some  authorities  claim  that  a  width  of  ^  incn 
is  sufficient  for  the  seat  of  a  conical  valve  4  inches  in  diameter.  The  valve  and  seat  are 
generally  made  of  composition  metal  for  marine  boilers,  but  in  Ashcroft's  valve  (see 
figure  3,  Plate  XXXIV.)  the  bearing-surfaces  are  formed  by  nickel  rings  let  into  the 
valve  and  seat. 

The  valve  is  guided  either  by  wings  attached  to  the  disc  below  its  seat  or  by  a  cen- 
tral spindle  Working  in  a  sleeve.  The  opinions  of  competent  engineers  differ  as  to  which 
of  these  two  devices  for  guiding  the  valve  is  preferable ;  both  are  liable  to  cause  the 
valve  to  stick  when  they  are  fitted  too  close,  in  consequence  of  the  lodgment  of  dirt  or 
scale,  or  of  unequal  expansion  when  steam  is  raised  quickly. 

To  prevent  the  canting  of  the  valve  in  consequence  of  the  oblique  thrust  thrown 
upon  it  by  the  lever  as  it  lifts,  the  central  spindle  upon  which  the  lever  rests  is  often 
detached  from  the  valve-disc  ;  the  latter  is  hollowed  out  on  the  top  so  that  the  point 
where  the  spindle  rests  upon  the  valve  lies  below  the  valve-seat.  When  this  spindle  is 
rigidly  attached  to  the  valve-disc  it  is  connected  with  the  lever  by  means  of  a  short 
link.  The  pins  or  bolts  of  the  articulated  joints  of  the  lever  and  link  are  often  made  of 
composition  to  lessen  the  liability  of  their  becoming  fast  by  rusting  or  by  getting 
clogged  with  grease  and  dirt.  To  reduce  the  friction  as  much  as  possible  it  is  best  to 
make  the  lever  turn  on  knife-edges,  case-hardened. 

The  lever  safety-valve  recommended  by  the  Board  of  Supervising  Inspectors  of 
Steam-vessels  is  represented  in  figure  2,  Plate  XXXIV.  The  following  directions  are 
given  regarding  its  construction : 

"All  the  points  of  bearing  on  lever  must  be  in  the  same  plane. 


SEC.  11.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  345 

"  The  distance  of  the  fulcrum  must  in  no  case  be  less  than  the  diameter  of  the  valve- 
opening. 

"The  length  of  the  lever  should  not  exceed  the  distance  of  the  fulcrum  multiplied 
by  ten. 

"  The  width  of  the  bearings  of  the  fulcrum  must  not  be  less  than  three-fourths  (£) 
of  one  inch. 

"  The  length  of  the  fulcrum-link  should  not  be  less  than  four  (4)  inches. 

"The  lever  and  fulcrum-link  must  be  made  of  wrought-iron  or  steel,  and  the  knife- 
edged  fulcrum-points  and  bearings  for  the  points  must  be  made  of  steel  and  hardened. 

"  The  valve,  valve-seat,  and  bushings  for  the  stem  or  spindle  must  be  made  of  com- 
position (gun-metal)  when  the  valve  is  intended  to  be  attached  to  a  boiler  using  salt 
water ;  but  when  the  valve  is  to  be  attached  to  a  boiler  using  fresh  water  and  generating 
steam  of  a  high  pressure,  the  parts  named,  with  the  exception  of  the  bushings  for  the 
spindle,  may  be  made  of  cast-iron. 

"The  valve  must  be  guided  by  its  spindle,  both  above  and  below  the  ground  seat 
and  above  the  lever,  through  supports  either  made  of  composition  (gun-metal)  or  bushed 
with  it. 

"  The  spindle  should  fit  loosely  in  the  bearings  or  supports. 

"  When  the  valve  is  intended  to  be*  applied  to  the  boilers  of  steamers  navigating 
rough  waters  the  fulcrum-link  may  be  connected  directly  with  the  spindle  of  the  valve, 
providing  always  that  the  knife-edged  fulcrum-points  are  made  of  steel  and  hardened, 
and  that  the  object  sought  by  the  link  is  obtained— viz.,  the  vertical  movement  of  the 
valve  unobstructed  by  any  lateral  movement. 

"In  all  cases  the  weight  must  be  adjusted  on  the  lever  to  the  pressure  of  steam  re- 
quired in  each  case  by  a  correct  steam-gauge  attached  to  the  boiler.  The  weight  must 
then  be  securely  fastened  in  its  position  and  the  lever  marked  for  the  purpose  of  facili- 
tating the  replacing  of  the  weight,  should  it  be  necessary  to  remove  the  same." 

Figure  1,  Plate  XXXIV.,  represents  the  form  of  safety-valve  used  on  the  boilers  of 
the  U.  S.  S.  Nipsic  represented  on  Plates  XII.  and  XXX. 

Figure  3,  Plate  XXXIV.,  represents  the  Ashcroft  spring  safety-valve  of  the  boilers 
of  U.  S.  S.  Adams  and  class.  One  valve  of  this  description,  3  inches  in  diameter,  was 
used  on  each  boiler  of  this  vessel.  In  addition  there  was  one  lever  safety-valve  of  ordi- 
nary construction,  having  a  diameter  of  10  inches,  which  was  connected  with  one  of  the 
main  steam-drums  and  had  an  arrangement  for  lifting  it  from  the  fire-room.  Each 
boiler  had  24  square  feet  of  grate-surface  and  598.6  square  feet  of  heating-surface,  and 
was  designed  for  a  working  pressure  of  80  Ibs.  per  square  inch  above  the  atmosphere. 


346  STEAM  BOILERS.  CHAP.  XV. 

The  Board  of  Trade  (England)  prescribes  that,  in  case  spring  safety-valves  are  used 
in  passenger-steamers,  there  must  be  fitted  to  each  boiler  at  least  two  separate  valves ; 
the  spring  and  valve  must  be  so  cased  in  that  they  cannot  be  tampered  with  ;  provision 
must  be  made  to  prevent  the  valve  flying  off  in  case  of  the  spring  breaking  ;  screw  lift- 
ing-gear must  be  provided  to  ease  all  valves,  if  necessary,  when  steam  is  up  ;  the  springs 
must  be  protected  from  the  steam  and  impurities  issuing  from  the  valves"-'  when  the 
valves  are  loaded  by  direct  springs  the  compressing-screw  must  abut  against  a  metal 
stop  or  washer  when  the  load  sanctioned  by  the  surveyor  is  on  the  valve  ;  the  size  of 
the  steel  of  which  the  spring  is  made  is  found  by  the  following  formula : 

D  =  diameter  or  side  of  square  of  the  wire,  in  inches  ; 

d  =  diameter  of  the  spring  from  centre  to  centre  of  wire,  in  inches ; 

S  =  load  on  the  spring,  in  pounds. 

Ic  =  constant  =  8,000  for  round  and  11,000  for  square  steel. 


The  accumulation  of  pressure  is  not  to  exceed  10  per  cent,  of  the  loaded  pressure. 


Fig.  139. 

H  j 

I  Q 

¥ 

t 

When  p  =  pressure  of  steam  in  pounds  per  square  inch  above  the  atmosphere, 
A  —  area  of  valve  in  square  inches, 
W  =  weight  of  the  load  applied  to  the  lever,  in  pounds, 
w  =  weight  of  the  lever  and  its  attachments,  in  pounds, 
GC  =  distance  of  centre  of  gravity  of  lever  from  fulcrum  C, 
10^  —  weight  of  valve  and  spindle,  in  pounds. 
DC  =  distance  of  axis  of  valve  from  fulcrum  C, 
BC  =  distance  of  centre  of  gravity  of  load  from  fulcrum  (7, 

the  steam-pressure  at  which  a  safety-valve  loaded  by  means  of  a  lever  (see  figure  139) 
will  open  is  found  by  the  formula : 


i  v  flC< 
P  =  ("   "^^     *^    +*0-^.     P.] 


SEC.  12. 


BOILER  MOUNTINGS  AND  ATTACHMENTS. 


347 


The  weight  of  the  load  required  with  a  lever  of  a  given  length  for  a  given  steam- 
pressure  is  found  by  the  formula : 


BG 

The  length  of  lever  required  with  a  given  weight  of  the  load  and  a  given  steam-pres- 
sure is  found  by  the  formula : 

(pX  A-w^DC-w&C 


W 


[III.] 


The  results  given  by  the  foregoing  formulae  are  modified  in  practice  by  the  friction 
of  the  articulations  and  of  the  stem,  and  the  position  of  the  weight  on  the  lever  must  be 
finally  adjusted  when  steam  is  on  the  boiler,  so  that  the  valve  lifts  at  the  required 
pressure. 


Fig.  140. 


Figure  140  represents  a  practical  method  of  weighting  a  safety-valve  lever,  taking 
into  account  the  load  due  to  the  weight  of  lever  and  valve  and  to  friction,  when  it  is  not 
convenient  to  adjust  the  valve  under  steam — viz.,  calculate  the  total  effective  pressure, 
p  X  A,  acting  on  the  valve ;  apply  at  the  end  of  the  lever  B  an  ordinary  weigh-beam, 
which  tends  to  raise  the  lever-arm  ;  adjust  the  load  P  on  the  weigh-beam  so  that  it  will 

fn     \/        A       "V*        7~)fy 

balance  a  weight  equal  to  —      fify      -•  then  adjust  the  weight  TFon  the  valve-lever 

till  it  brings  the  lever  and  the  weigh-beam  into  a  horizontal  position. 
12.  Miscellaneous  Attachments  of  Boilers. 

^Escape-pipes. — The  steam  discharged  by  the  safety-valves  and  by  the  exhaust  of 
the  steam-pumps  and  other  auxiliary  engines  is  conducted  to  the  escape-pipe  and  from 
it  discharged  into  the  atmosphere.  There  are  one  or  several  escape-pipes,  which  are  car- 
ried up  alongside  the  smoke-pipe  to  a  greater  or  less  height  above  the  upper  deck. 


348  STEAM  BOILERS.  CHAP.  XV. 

With  a  hoisting  chimney  the  escape-pipe  reaches  either  only  to  the  top  of  the 
stationary  section  of  the  chimney,  or  it  is  made  telescopic,  having  a  movable  section 
attached  to  the  movable  section  of  the  chimney,  which  slides  within  the  lower  station- 
ary section,  the  latter  being  provided  with  a  stuffing-box  at  its  upper  end. 

The  escape-pipe  is  generally  made  of  copper.  Its  upper  end  is  either  simply  made 
flaring  or  it  is  provided  with  an  arrangement  for  intercepting  the  water  which  is  carried 
up  with  the  steam  (see  figure  141). 

Fig.  HI.  ^e  U-  S.  S.  Nlpsio  has  a  single  escape-pipe,  9  inches  in  diameter, 

which  is  carried  up  at  the  forward  side  of  the  chimney  to  the  top  of 
the  stationary  section.  The  safety-valve  chambers  of  the  boilers  on 
each  side  of  the  vessel  are  connected  with  each  other  by  pipes  5f 
inches  in  diameter,  and  communicate  with  the  escape-pipe  by  means 
of  a  branch-pipe  7  inches  in  diameter.  These  pipes  are  made  of  cop- 
per, No.  14  B.  W.  G.  thick,  and  are  connected  by  composition  flanges. 
The  exhaust-pipes  of  auxiliary  engines  should  be  connected  directly 
with  the  escape-pipe,  and  not  with  any  of  the  safety-valve  chambers, 
as  is  often  done  in  order  to  effect  a  saving  in  the  length  of  the  pipes, 
because  the  steam  and  condensed  water  leaking  through  the  safety-valve  will  keep  the 
boiler  damp  when  it  is  not  in  use. 

Justice's  quieting-chamber  is  designed  to  prevent  the  deafening  noise  produced  by 
steam  issuing  from  safety-valves,  from  the  exhaust  of  high-pressure  engines,  etc.  The 
chamber,  which  is  either  cylindrical  or  of  any  other  convenient  shape,  is  filled  with 
balls  of  suitable  material  and  of  proper  size,  confined  compactly  between  copper  grat- 
ings ;  for  low  pressures  balls  or  beads  of  annealed  glass  are  found  best,  while  for  high 
pressures  hollow  copper  or  brass  balls  of  small  size  are  used.  The  current  of  steam 
flowing  through  this  chamber  is  broken  up  into  numerous  streamlets  in  its  passage 
through  the  tortuous  interstices  formed  by  the  balls.  The  vibrations  produced  in  the 
several  balls  by  the  impact  and  friction  of  the  steam  are  not  uniform  and  interfere  with 
one  another,  and  thus  do  not  produce  sound.  By  making  the  total  area  of  the  open- 
ings sufficiently  large  the  steam  is  allowed  to  escape  without  an  appreciable  increase  of 
back-pressure.  The  area  of  the  exit-opening  is  always  in  excess  of  that  of  the  inlet- 
pipe.  The  cross-area  of  the  chamber  is  proportioned  to  the  pressure  and  volume  of  the 
steam ;  the  diameter  of  the  chamber  is  from  five  to  six  times  the  diameter  of  the  escape- 
pipe.  The  depth  of  the  chamber  is  about  8  inches  for  all  sizes. 

Figure  142  shows  a  sectional  elevation  of  a  quieting-chamber,  which  communicates 
below  with  a  safety-valve  and  above  with  the  escape-pipe.  The  safety-valve,  which  is 


SEC.  12. 


BOILER  MOUNTINGS  AND  ATTACHMENTS. 


349 


placed  on  the  main  steam-pipe  between  the  boilers  and  a  stop-valve,  can  be  opened  by 
means  of  a  hand-lever,  and  discharges  the  steam  through  the  quieting-chamber  into  the 
escape-pipe. 

Figure  143  is  a  sectional  elevation  of  another  form  given  to  the  quieting-chamber. 
The  latter  has  a  central  pipe  passing  through  it,  which  is  provided  with  a  valve,  so  that 
the  steam  may  be  discharged  either  through  the  chamber  or  directly  into  the  escape- 
pipe.  The  valve  may  be  loaded  to  discharge  the  steam  automatically,  or  it  may  be 
lifted  by  a  hand-lever. 

Similar  quieting-chambers  are  introduced  between  the  blast-pipes  and  nozzles  of 
locomotives,  steam-launches,  torpedo-boats,  etc. 


Fig.  143. 


In  Shaw's  noise-quieting  nozzle  the  steam  escapes  through  cylindrical  coils  of  wire, 
the  diameter  and  length  of  the  coils  being  such  that,  when  compressed  nearly  to  contact, 
the  spaces  between  the  turns  of  the  coils  will  make  a  total  area  of  opening  much  greater 
than  that  of  the  steam  escape-pipe.  As  the  individual  turns  of  the  wire  coils  cannot 
vibrate  without  coming  in  contact  with  the  adjacent  ones,  interference  and  consequent 
silence  results  in  the  same  way  as  two  vibrating  piano- wires,  if  brought  together,  will 
immediately  destroy  each  other's  sound.  The  spirals  are  opened  wider  by  any  increase 
of  steam  passing  through,  and  this  action,  as  well  as  the  tremulous  motion  of  the  spirals 
produced  by  the  issuing  steam,  prevents  their  clogging  by  an  accumulation  of  foreign 


350 


STEAM  BOILERS. 


CHAP.  XV. 


matter.  The  spiral  coils  are  made  of  brass  wire  about  f-  inch  thick,  and  are  from  4  to  5 
inches  long.  A  greater  or  less  number  of  coils  are  arranged  in  various  ways  for  each 
escape-pipe. 

Figure    144     represents     Shaw's 

noise-quieting    nozzles    arranged    in 

clusters  for  large  steamships.     P  is 

the  escape-pipe  from  safety-valve,  on 

which  the  casing  D,  containing  the 

cluster  of  nozzles,  is  bolted.     G  are 

nozzles  of  spiral  wire,  having  a  solid 

top,  and  secured  to  elbows,  J,  that 

are  connected  with  the  escape-pipe 

P.    The  steam  escapes  through  the 

wire  coils  into  the  casing  D,  whence 

it  is  led  to  the  escape  pipe  F. 

Figure  145  represents  a  sectional 

elevation  and  top  view  of  another  ar- 
rangement of  the  noise-quieting  noz- 
zle. The  nozzle  is  made  entirely  of 

brass  and  copper.     The  bottom  flange 

connects  with  the  escape-pipe  close  to 

the  safety-valve.    The  steam  escaping 

from  the  safety-valve  is  conducted 

into  the  base  B  and  into  a  central 

tube,   C,  where  it  is  distributed  to 

numerous  coils  of  brass  wire,  F,  secured  in  the  top  plate 
of  base  B  and  in  the  central  tube  C.  Escaping  between 
the  turns  of  these  coils,  the  steam  enters  the  copper  casing 
P,  from  which  it  is  conducted  through  the  regular  escape- 
pipe  to  the  outer  air.  A  valve,  Gr,  is  sometimes  provided  at 
the  top  of  the  central  pipe  C,  said  valve  being  loaded  with 
about  2  Ibs.  pressure,  which  guarantees  a  sufficient  outlet 
without  reference  to  the  coils  F ;  but  this  valve  is  not  a 
necessity,  as  abundant  area  of  outlet  exists  in  the  brass 
coils  F. 


oooUooo 
ooooooo 

30OOOOO 
IOOOOOO 

ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 


Fig.  145. 


Bleeding  valves  and  pipes  are  intended  to  pass  waste  steam  into  the  condenser  in- 


SBC.  13.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  351 

stead  of  blowing  it  off  through  the  safety-valve.  For  this  purpose  a  copper  pipe,  hav- 
ing a  diameter  of  about  4  inches,  leads  from  the  main  steam-pipe  to  a  stop-valve  on  the 
top  of  the  condenser,  another  stop- valve  being  placed  between  the  main  steam-pipe  and 
the  bleeding-pipe. 

The  reverse  or  vacuum  valve  is  a  small  safety-valve  opening  inwards,  designed  to 
open  and  thus  prevent  the  collapse  of  a  boiler  in  case  the  pressure  within  the  boiler 
falls  below  the  atmospheric  pressure.  These  vacuum-valves  were  generally  attached  to 
boilers  as  long  as  steam  of  very  low  pressure  was  used  and  the  shell  of  boilers  was  pro- 
portionately weak,  but  they  are  seldom  used  nowadays. 

Stop-valves  and  steam-pipes  are  attached  directly  to  the  boilers  to  supply  the  steam- 
pumps  and  other  auxiliary  engines,  the  distiller,  steam-whistle,  and  steam-blast  with 
steam  when  communication  between  the  main  steam-pipe  and  the  boilers  is  shut  off. 

Drain-cocks  are  fitted  to  the  bottom  of  the  boilers,  to  superheating-chambers  and 
steam-drums,  and  to  all  valve-chambers  and  pipes  where  water  is  liable  to  lodge  after 
the  boilers  are  emptied. 

In  the  U.  S.  S.  Nipsic  the  drain-pipes  discharge  the  waste  water  into  a  cylindrical 
wrought-iron  tank  placed  in  the  spandrel  under  the  after  boiler.  The  several  drain- 
pipes communicate  with  a  common  pipe,  which  is  connected  to  a  stop- valve  placed  on 
the  top  of  the  tank.  Another  pipe,  which  is  likewise  provided  with  a  stop-valve,  takes 
the  water  from  the  bottom  of  the  tank  to  the  feed-pumps.  A  gauge-glass  shows  the 
height  of  the  water  in  the  tank. 

13.  Covering  for  Boilers. — The  saving  in  fuel  which  may  be  effected  by  prevent- 
ing the  loss  of  heat  by  radiation  and  convection  from  the  shell  of  boilers,  steam-pipes, 
etc.,  has  been  discussed  in  section  6,  chapter  iii.  Besides  the  economic  advantage 
resiilting  from  surrounding  boilers  with  non-conducting  materials,  the  reduction  of  the 
temperature  in  the  confined  spaces  around  the  engines  and  boilers  of  a  vessel  is  of  great 
importance.  It  is  also  necessary,  especially  in  single-deck  vessels,  to  provide  a  tight 
covering  for  the  top  of  boilers  to  protect  them  from  the  water  which  may  leak  through 
the  deck. 

The  principal  methods  used  for  protecting  the  shells  of  marine  boilere  are  the  follow- 
ing :  the  boilers  are  surrounded  with  an  air-tight  casing  enclosing  an  air-space  ;  or  they 
are  covered  with  hair-felt  or  other  loose,  fibrous  material,  held  in  place  by  an  outer  cas- 
ing ;  or  they  receive  a  thick  coating  of  some  cement  applied  like  plaster  to  their  surfaces. 
Sometimes  several  of  these  methods  are  used  in  combination.  These  different  methods 
of  covering  can  be  made  equally  effective,  as  far  as  the  prevention  of  loss  of  heat  from 
the  covered  surface  is  concerned,  provided  the  casing  is  fitted  with  sufficient  exactness 


352  STEAM  BOILERS.  CHAP.  XV. 

and  the  covering  or  coating  is  applied  in  sufficient  thickness.  Their  relative  value  is, 
therefore,  to  be  measured  by  the  weight,  the  first  cost  and  the  durability  of  the  cover- 
ing, and  by  the  facility  with  which  it  can  be  removed  and  replaced  for  the  purpose  of 
examining  and  repairing  the  covered  parts. 

The  entire  cylindrical  shell  and  the  back  of  the  boilers  of  the  U.  S.  S.  MiantonomoTi 
and  class  are  covered  with  an  air-tight  casing  of  galvanized  iron,  enclosing  an  air-space 
of  1J  inches  between  the  boiler  and  the  casing.  (See  Specifications  of  Boilers  of  U.  S.  S. 
MiantonomoTi  and  class,  section  10,  chapter  vii.) 

Cow-hair  felt,  stitched  on  canvas,  weighing  1  pound  per  square  foot  when  \\  inches 
thick,  has  usually  been  employed  for  covering  the  boilers  of  United  States  naval  ves- 
sels. The  specifications  for  the  cylindrical  boilers  of  the  U.  S.  S.  Adams  and  class  pre- 
scribe that  "after  the  boilers  are  in  the  vessel,  have  been  tried  with  steam,  and  all 
leaks  have  been  made  tight,  the  boilers  are  to  be  covered  with  felting  \\  inches  thick, 
strongly  stitched  to  No.  1  canvas,  and  secured  by  four  hoops,  2  inches  wide,  encircling 
the  boiler ;  and  over  this  is  to  be  placed  sheet-lead  of  No.  14  wire-gauge,  securely  sol- 
dered at  all  edges." 

Rectangular  boilers  are  covered  in  this  manner  on  the  top,  and  on  the  back  and  sides 
for  some  distance  down ;  the  temperature  of  the  water  in  the  lower  part  of  the  boiler 
is  generally  so  much  less  than  the  temperature  of  the  steam  that  it  is  not  necessary 
to  extend  the  covering  to  the  bottom  of  the  boiler.  On  the  felting  is  frequently  placed 
a  covering  made  of  wooden  staves,  tongued  and  grooved.  The  manner  of  securing  the 
wood  casing  to  launch-boilers  is  shown  on  Plate  XVI.  On  steam-pipes  these  staves 
are  generally  held  together  by  brass  hoops  drawn  together  by  a  single  bolt. 

When  steam  of  more  than  45  pounds  pressure  is  used  its  temperature  is  sufficient 
to  char  the  felt  when  it  comes  in  immediate  contact  with  the  metal  of  the  boiler.  On 
this  account  various  contrivances  have  been  designed  for  maintaining  a  narrow  air-space 
between  the  felt  and  the  boiler,  and  asbestos  boards  or  other  mineral  substances  of 
low  thermal  conductivity  are  sometimes  placed  between  the  boiler  and  the  felt. 

Various  mastic  compositions  of  clayey  material,  and  cements  containing  an  admix- 
ture of  asbestos  in  greater  or  less  proportions,  are  applied  like  plaster  either  directly 
to  the  surface  of  the  boiler-shell  or  to  a  wire  netting  stretched  over  the  latter.  The 
weight  of  such  a  covering  is  considerable.  The  most  serious  objection  to  its  use  on 
steam-chambers  is  the  difficulty  of  removing  and  replacing  it  for  the  purpose  of  examin- 
ing the  covered  parts. 

'•'•Mineral  wool"  is  a  loosely-cohering,  fibrous  substance  resembling  coarse  wool, 
formed  by  blowing  a  jet  of  steam  into  a  stream  of  fluid  slag.  It  is  used  as  a  non-con- 


SEC.  14.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  353 

ductor  by  packing  it  in  a  space  formed  around  the  protected  vessel  by  an  outer  casing. 
It  sometimes  contains  foreign  substances  which  attack  the  iron  under  the  influence  of 
heat  and  moisture. 

14.  Feed-water  Heaters  and  Filters. — Feed-water  heaters  are  designed  to  utilize 
waste  heat  and  to  lessen  the  difference  of  the  temperatures  of  the  steam  and  water  in 
the  boiler.  The  latter  is  an  important  consideration ;  the  introduction  of  a  mass  of 
cold  water  in  a  highly -heated  boiler  causes  injurious  local  contractions,  and  the  diffe- 
rence of  the  temperatures  in  the  top  and  bottom  of  cylindrical  boilers,  amounting  often 
to  from  100°  to  200°  Fahr.,  produces  often  far  greater  strains  than  those  due  to  the 
steam-pressure. 

The  saving  of  heat  effected  by  the  use  of  heaters,  in  per  centum  of  the  total  heat 
expended,  may  be  expressed  by  the  formula  : 

.*.-* 
"  T—  t' 

where  t,  £„  and  T  are  the  temperatures  of  the  feed-water  before  and  after  it  passes 
through  the  heater,  and  the  total  heat  of  an  equal  weight  of  steam,  respectively. 
This  saving  may  be  in  many  cases  to  a  great  extent  counterbalanced  by  the  cost  and 
weight  of,  and  the  space  occupied  by,  the  heater,  and  by  the  additional  cost  and  labor 
required  to  keep  it  in  order. 

When  the  temperature  of  the  escaping  gases  in  the  boiler-uptake  exceeds  the  limit 
given  in  section  11,  chapter  ii.,  the  economic  and  potential  evaporative  efficiency  of  the 
boiler  will  be  increased  by  utilizing  the  excess  of  heat  in  raising  the  temperature  of  the 
feed- water.  With  a  well-designed  boiler  this  should  not  be  necessary,  and  the  arrange- 
ment of  the  heater- pipes  in  the  uptake  of  a  marine  boiler  presents  many  difficulties 
and  inconveniences. 

When  the  engines  are  fitted  with  a  jet-condenser,  and  the  boilers  are  fed  with  salt 
water,  heaters  are  used  to  advantage  to  impart  to  the  feed- water  a  portion  of  the  heat 
contained  in  the  supersalted  water  which  is  blown  off  to  reduce  the  saturation  of  the 
boiler.  In  the  U.  S.  S.  Wabash  each  boiler,  containing  83.5  square  feet  of  grate-sur- 
face, was  provided  with  a  heater  lying  beneath  the  floor-plates  of  the  fire-room.  This 
heater  was  composed  of  a  cast-iron  cylindrical  shell,  12£  inches  in  external  diameter, 
containing  31  brass  tubes  \\  inches  in  external  diameter  and  13  feet  long.  The  super- 
salted  water  of  the  boiler  was  blown  off  continuously  from  the  surface  by  a  cock  and 
pipe,  and  passed  around  the  tubes  on  its  way  to  the  sea,  while  the  continuous  feed 
passed  through  these  tubes  on  its  way  from  the  hot- well  to  the  boiler.  When  the 


354  STEAM  BOILERS.  CHAP.  XV. 

water  of  the  boiler  was  kept  at  a  density  of  If  thirty-seconds  the  feed-water  received 
an  accession  of  temperature  of  about  30°  Fahr. 

With  non-condensing  engines  the  exhaust  steam  may  be  used  to  heat  the  feed-water. 
The  steam  is  either  blown  into  an  open  tank,  where  it  mingles  with  and  is  condensed  by 
a  shower  of  water,  or  the  heater  is  constructed  on  the  principle  of  a  surface-conden- 
ser— the  steam  being  condensed  as  it  passes  through  a  nest  of  tubes  around  which 
the  feed-water  circulates. 

The  Berryman  heater  consists  of  a  closed  cylindrical  wrought-iron  tank,  the  bottom 
of  which  is  bolted  to  a  casting  divided  by  a  partition  into  two  compartments.  The  inte- 
rior of  the  tank  is  occupied  by  a  number  of  siphon-shaped  brass  tubes,  which  are  se- 
cured with  both  ends  in  the  bottom  plate  of  the  tank  in  such  a  manner  that  their  ends 
communicate  with  either  compartment  of  the  lower  casting.  The  exhaust  steam  enters 
one  of  these  compartments,  and,  after  parting  with  its  heat  in  passing  through  the  tubes, 
it  is  discharged  from  the  other  compartment.  The  feed-water  is  forced  by  the  pump 
into  the  tank  near  the  bottom,  and  passes  out  through  an  opening  at  the  top.  With 
this  arrangement  the  warmest  water  rises  naturally  to  the  top  and  passes  off  to  the 
boiler,  and  foreign  matter  held  in  suspension  in  the  feed-water  has  a  chance  to  settle 
in  the  bottom  of  the  tank. 

Filters. — United  States  naval  boilers  using  high  pressures  of  steam  have  been  fitted 
with  feed-water  filters  consisting  of  a  tank  divided  by  screens  into  several  compartments, 
which  are  filled  with  various  substances  for  filtering  the  water  or  neutralizing  the  fatty 
acids  contained  in  it. 

In  Selderi*  s  filter,  as  fitted  to  the  U.  S.  S.  Miantonomo7t,  the  water  coming  from  the 
hot- well  enters  at  the  top  of  a  tank,  and  passes  through  a  vertical  partition  formed  by  a 
sheet  of  Burlap  cloth  placed  between  two  wire  screens  into  an  upper  compartment  which 
is  filled  with  coke.  The  plate  forming  the  bottom  of  this  compartment  is  perforated  at 
one  end  with  62  f -inch  holes,  through  which  the  water  passes  into  the  lower  compart- 
ment, which  is  filled  with  sponge.  The  bottom  plate  of  this  compartment  has  an  equal 
number  of  holes  near  the  opposite  side  of  the  tank,  through  which  the  water  flows 
into  the  channel-way,  whence  it  is  withdrawn  by  the  feed-pump.  Doors  are  provided 
for  removing  the  screens,  the  coke,  and  the  sponge  for  the  purpose  of  cleaning  or  renew- 
ing them. 

15.  Feed-pumps  and  Injectors. — When  the  boilers  are  fed  with  fresh  water  the 
weight  of  water  evaporated  as  a  maximum  is  the  least  quantity  which  the  feed-pump 
must  be  capable  of  delivering  in  a  given  time ;  when  sea-water  is  used  the  weight  of 
water  to  be  blown  off  to  maintain  the  water  in  the  boiler  at  the  proper  density  has  to  be 


SEC.  15.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  355 

added  to  the  weight  of  water  evaporated  in  a  given  time.  The  feed-pump  should,  how- 
ever, be  capable  of  discharging  about  twice  the  quantity  of  water  evaporated  and  blown 
off  in  a  unit  of  time,  in  order  to  supply  losses  due  to  priming  and  leakage  and  to  make 
allowances  for  irregularities  in  the  working  of  the  pump. 

In  calculating  the  dimensions  of  a  pump  it  may  be  assumed  that  the  volume  of  the 
water  discharged  is  ordinarily  about  75  per  cent,  of  the  space  displaced  by  the  plunger 
per  stroke  of  pump. 

According  to  the  foregoing  rule  the  capacity  of  the  main  feed-pump  connected  with 
the  engines  is  to  be  calculated,  as  well  as  the  least  capacity  of  the  auxiliary  steam- 
pump.  But  it  is  advantageous  to  increase  the  dimensions  of  the  latter  pump  so  that  it 
may  be  worked  at  a  low  speed  ;  because  with  a  slow- working  pump  shocks  in  the  feed- 
pipes are  avoided,  and  the  hammering  action  of  the  check-valves  is  lessened,  and  the 
volume  of  water  discharged  relatively  to  the  space-displacement  of  the  piston  is  in- 
creased. 

The  feed-water  Injector  was  invented  by  Giffard,  a  French  engineer,  in  the  year 
1858.  In  its  simplest  form  (see  figure  146)  the  injector  consists  of  a  pipe,  A,  for  the  ad- 
mission of  steam,  which,  escaping  through 
the  conical  nozzle  of  the  receiving-tube  C 
at  a  high  velocity,  is  joined  by  water 
which,  flowing  in  through  the  pipe  B, 
mingles  with  and  condenses  the  steam  in 
the  conical  combining -tube  D.  The  con- 
densed steam  gives  an  impulse  to  this  water,  which  is  driven  in  a  continuous  stream 
through  the  delivery-tube  H  and  the  check- valve  J  into  the  boiler,  provided  it  possesses 
sufficient  velocity.  During  the  passage  of  the  water  from  D  to  H  it  is  driven  across  the 
space  F,  called  the  overflow,  which  communicates  by  means  of  the  over/low-nozzle  G 
with  the  outside  air.  If  too  much  water  is  supplied  to  the  steam  some  water  may 
escape  at  this  point  and  flow  out  through  the  overflow-nozzle  ;  if  there  be  too  little 
water  air  will  be  drawn  in  at  G  and  carried  into  the  boiler  with  the  water. 

The  fact  that  a  mass  of  steam  should  be  capable  of  imparting  to  a  much  larger  mass 
of  water  sufficient  velocity  to  overcome  even  a  higher  pressure  than  that  which  caused 
the  original  motion  of  the  relatively  small  mass  of  steam,  has  frequently  been  looked 
upon  as  a  paradox.  This  action  of  the  injector  depends  on  the  following  prin- 
ciples : 

The  change  in  the  molecular  condition  of  the  steam  by  condensation  does  not  affect 
the  motion  of  its  particles.  The  mass  of  condensed  steam,  moving  with  its  original  high 


856  STEAM  BOILERS.  CHAP.  XV. 

velocity,  produces  a  concentrated  effect  by  its  impact  on  the  mass  of  the  condensing 
water ;  and  the  resultant  momentum  of  the  two  unelastic  fluids  is  equal  to  the  sum 
of  the  momenta  of  their  masses  before  the  impact.  (See  equation  [II.]) 

An  injector  made  as  shown  in  figure  146  is  known  as  a  fixed-nozzle  injector.  With 
a  given  steam-pressure  it  will  give  a  constant  feed  of  a  given  quantity.  To  adapt  the 
instrument  to  variations  in  the  steam-pressure,  and  to  effect  variations  in  the  quantity 
of  feed- water  delivered,  the  areas  of  the  openings  of  the  conical  nozzles  have  to  be 
altered  in  order  to  diminish  or  increase  the  steam  or  water  supply.  This  adjustment 
was  an  essential  feature  of  Giffard's  injector.  It  is  usually  effected  by  means  of  a  taper- 
ing spindle  which  can  be  raised  or  lowered  by  means  of  a  screw  within  the  receiving- 
tube,  and  by  making  either  the  receiving-tube  or  the  combining-tube  movable,  so  that 
by  raising  or  lowering  the  same  the  annular  space  between  the  receiving-nozzle  and  the 
combining-tube  is  either  enlarged  or  contracted.  In  the  fixed-nozzle  injectors  the  ad- 
mission of  steam  and  water  is  regulated  by  stop-valves  in  the  supply -pipes ;  but  the 
range  of  these  instruments,  as  far  as  steam-pressure,  temperature,  and  quantity  of 
feed-water  are  concerned,  is  much  more  limited  than  that  of  the  adjustable  in- 
jectors. 

The  first  action  of  the  steam-jet  issuing  from  C  (see  figure  146)  is  to  drive  the  air  out 
of  the  tube  D,  thus  forming  a  more  or  less  perfect  vacuum  in  the  chamber  surrounding 
the  nozzle  C,  in  consequence  of  which  the  water  will  be  lifted  to  a  greater  or  less 
height  in  the  supply-pipe.  This  lifting  power  of  the  injector  may  be  greatly  improved 
by  giving  to  the  openings  suitable  forms  and  dimensions.  The  water  is  frequently 
lifted  from  6  to  8  feet ;  and  it  is  claimed  that  with  some  large  injectors  of  improved  form 
a  lift  of  18  feet  has  been  obtained.  The  water  to  be  lifted  must  be  free  from  air,  and 
its  initial  temperature  must  be  less  than  the  boiling-point  of  water  under  the  dimin- 
ished pressure  existing  in  the  chamber  surrounding  C.  Therefore,  when  a  feed-water 
heater  is  to  be  used  in  connection  with  an  injector,  it  is  better  to  place  it  between  the 
latter  and  the  boiler. 

The  quantities  of  steam  and  water  admitted  must  be  so  regulated  that  the  jet  of 
steam  is  completely  condensed ;  otherwise  a  certain  quantity  of  vapor  will  enter  the 
chamber  F  and  escape  into  the  atmosphere,  proving  a  complete  loss.  The  temperature 
of  the  water-jet  issuing  from  D  must  be  less  than  212°  Fahr.,  otherwise  the  water  will 
vaporize  as  it  is  brought  into  communication  with  the  atmosphere  in  passing  from  D  to 
H.  The  steam  must  be  perfectly  dry  to  give  the  best  results. 

The  relation  existing  between  the  quantities  of  water  and  steam  admitted,  and  their 
respective  temperatures,  is  expressed  by  the  following  equation  : 


SEC.  15.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  357 

Calling  t  —  final  temperature  of  the  feed-water  discharged  at  H, 
S  —  initial  temperature  of  the  feed-  water  entering  at  B, 
T—  total  heat  contained  in  a  pound  of  steam, 
Q  =  weight  of  steam  in  pounds  expended  in  a  unit  of  time, 
q  =  weight  of  water  entering  at  B  in  a  unit  of  time, 

we  have  (Q+q)  t  =  Q  T+qS; 

hence  Q(T-f)  =  q(t  -  S)  ; 

tL-T^L      [I] 
Q  "  t-* 

As  the  quantity  Ovaries  little  with  the  pressure  of  the  steam,  the  value  of  the  pro- 
portion ^~  depends  principally  upon  t  and  $  —  that  is,  the  final  and  initial  temperatures 

V 

of  the  feed-water. 

Neglecting  the  effect  of  friction  and  other  disturbing  influences  occurring  in  practice, 
the  relation  existing  between  the  velocities  of  the  steam-jet  and  water-jet  is  expressed 
by  the  following  equation,  in  which 

v  =  the  velocity  of  the  mass  of  steam  Q  issuing  from  the  receiving-tube  ; 

U  =  the  initial  velocity  of  the  mass  of  water  q  entering  at  B  ; 

W  =  the  velocity  of  the  water-jet  issuing  from  the  combining-tube  : 

«o  (Q  +  4)  =  Qv-\-qu; 
Qv  +  qu        n] 


Calling  F  —  the  cross-area  of  the  nozzle  of  the  receiving-tube, 

FI  =  the  cross-area  of  the  larger  orifice  of  the  combining-tube, 

G  =  the  cross-area  of  the  nozzle  of  the  combining-tube, 

(?,  =  the  cross-area  of  the  feed-pipe, 

w,  =  the  velocity  of  the  water  passing  through  GH 

m  =  the  specific  volume  of  the  steam, 

we  can  represent  the  mass  of  water  delivered  in  a  unit  of  time  by  the  following  ex- 
pressions : 

Q  +  q  =  Gw  =  Glwl  =  ^  +  Flu.     [III.] 

The  water-jet  entering  the  boiler  must  perform  the  same  amount  of  work  as  an  equal 
mass  of  water  issuing  from  the  boiler  under  the  pressures  existing  within  the  boiler 


358  STEAM  BOILERS.  CHAP.  XV. 

and  the  injector  would  be  capable  of  doing.      This  is  expressed  by  the  following 
equation  : 


where  h  =  the  height  of  a  column  of  water  representing  the  absolute  steam-pres- 

sure in  the  boiler  ; 
ht  =  the  height  of  the  nozzle  of  the  receiving-tube  above  the  water-level 

within  the  boiler  ; 
x  =  the  height  of  a  column  of  water  representing  the  absolute  pressure  of 

the  water  at  the  mouth  of  the  combining-  tube. 

Calling  Tc  =  the  height  of  a  column  of  water  representing  the  atmospheric  pressure, 
A,  =  the  height  to  which  the  water  is  lifted, 

u* 

we  have  Jc  —  h,  —  x  =  -^  —  .    [V.] 


(See  Weisbach,  '  I/eTirbuch  der  Ingenieur  und  MascMnen-MecJianiTcJ  dritter  The/I 
II.  Abtheilung.) 

By  means  of  the  foregoing  equations  the  duty  of  an  injector  under  given  conditions, 
and  the  cross-area  of  the  openings  of  the  various  parts  of  an  injector  for  a  given  duty, 
may  be  calculated. 

The  causes  decreasing  the  efficiency  of  injectors  are  friction,  the  shocks  experienced 
by  the  water  in  the  passages,  the  incomplete  condensation  of  the  steam  and  the  admix- 
ture of  air  with  the  water-  jet,  and  the  waste  of  water  at  the  overflow. 

The  least  quantity  of  water  which  can  be  delivered  by  an  injector  is  generally  not 
less  than  60  per  cent,  of  the  largest  quantity  delivered  under  the  same  conditions  of 
temperature  and  pressure. 

Experiments  made  in  the  year  1879  on  Irwin's  injector  (see  Franklin  Institute  Jour- 
nal, February,  1880)  indicate  that  on  the  whole  the  ratio  of  the  weight  of  water  de- 

livered to  the  weight  of  steam  used  (or  -$-.  of  equation  [I.])  decreased  as  the  pressure  of 

Tb/ 

steam  increased  from  15  to  105  pounds  per  sq.  inch  above  the  atmosphere  ;  that,  on  the 
contrary,  the  work  done,  expressed  in  foot-pounds  per  pound  of  steam,  increased  under 
the  same  conditions,  the  water  being  delivered  in  every  case  against  a  pressure  equal  to 

that  of  the  steam  used  ;  that  the  ratio  Q-  decreased  likewise  when  the  delivery  of  water 

V 

was  less  than  the  maximum  for  the  pressures  and  temperatures  of  steam  and  water. 
The  largest  amount  of  work  was  done  when  the  steam  and  water  pressures  were  90 


SBC.  15.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  359 

pounds  per  square  inch  above  the  atmosphere,  and  the  injector  delivered  15.71  Ibs.  of 
water,  supplied  under  a  head  of  6£  inches,  per  pound  of  steam  ;  the  work  done  in  this 
case  being  equal  to  3449.94  foot-pounds  per  pound  of  steam  used.  Assuming  that  a 
pump  uses  from  £•  to  1£  Ibs.  of  steam  for  every  33,000  Ibs.  of  water  lifted  one  foot  high, 
the  highest  efficiency  of  the  injector  in  the  above  experiments  was  nearly  from  13  to 
6.5  times  less  than  the  efficiency  of  a  steam-pump.  Since,  however,  in  the  injector 
nearly  all  the  heat  of  the  steam  which  is  not  converted  into  mechanical  work  is  utilized 
in  raising  the  temperature  of  the  feed- water,  the  injector  compares  favorably  with  a 
steam-pump  as  a  feed  apparatus. 

There  are  certain  inconveniences  connected  with  the  use  of  injectors  which  have  pre- 
vented its  general  adoption  as  a  feed  apparatus  for  marine  boilers — viz.,  the  rolling  of 
the  ship  is  apt  to  cause  a  break  in  the  water- jet ;  the  foaming  of  the  boilers  interferes 
with  its  action ;  it  is  easily  disarranged  by  particles  of  salt  or  other  solid  matter  en- 
trained by  the  steam  or  the  feed- water ;  any  air  entering  through  the  overflow  spoils  the 
vacuum  of  the  condenser.  Besides,  all  steam- vessels  must  carry  steam-pumps  for  vari- 
ous purposes,  so  that  the  addition  of  injectors  is  unnecessary. 

The  difficulty  of  making  by  hand  the  proper  adjustments  regulating  the  admission 
of  steam  and  water,  which  become  necessary  whenever  the  steam-pressure  changes,  led 
to  the  introduction  of  the  self-adjusting  injector,  manufactured  by  William  Sellers  & 
Co.,  Philadelphia  (see  figure  2,  Plate  XXXV.)  The  upper  end  of  the  combining-tube 
G  is  made  in  the  form  of  a  piston,  which  slides  freely  in  the  exterior  case  ;  the  lower 
part  of  the  combining-tube  is  guided  by  a  sleeve  on  the  upper  end  of  the  delivery-tube 
D.  The  overflow- valve  is  closed  as  soon  as  the  apparatus  begins  to  work ;  if  now  the 
water-supply  becomes  too  great  a  portion  of  the  water  escapes  by  the  opening  O  in  the 
upper  part  of  the  delivery-tube,  and,  accumulating  in  the  chamber  surrounding  the 
combining-tube,  presses  under  the  piston  and  raises  the  combining-tube  ;  on  the  other 
hand,  when  the  feed-supply  is  insufficient  a  partial  vacuum  is  formed  under  the  piston, 
and  the  combining-tiibe  is  forced  down  till  the  increased  feed-supply  establishes  equili- 
brium on  both  sides  of  the  piston.  In  this  manner  the  instrument  regulates  automati- 
cally the  water-supply  so  as  to  give  always  the  best  result  with  the  pressure  and  weight 
of  steam  used,  and  the  indraught  of  air  and  waste  of  water  at  the  overflow  is  avoided. 

The  conical  spindle  which  regulates  the  flow  of  steam  in  the  receiving-tube  is  per- 
forated by  a  narrow  passage  bored  along  its  axis,  which  communicates  with  the  steam- 
space  through  grooves  at  the  screwed  end,  when  the  valve  W,  formed  by  an  enlargement 
of  the  spindle,  is  raised.  The  valve  W  seats  on  the  upper  side  of  a  second  valve,  X, 
which  in  turn  seats  on  the  receiving-tube  A.  The  small  jet  of  steam  which  escapes 


360 


STEAM  BOILERS. 


CHAP.  XV. 


through  the  passage  in  the  spindle  before  the  valve  X  is  raised  is  more  effective  in  ex- 
hausting the  air  and  lifting  the  water  in  the  supply-pipe  than  a  jet  escaping  through 
the  narrow  annular  space  between  the  taper  plug  and  the  receiving-nozzle. 

With  this  central  jet  water  is  raised  from  10  to  18  feet  in  the  supply-pipe,  according 
to  the  size  of  the  instrument. 

To  start  the  instrument  the  lever  K  is  drawn  back  a  short  distance  till  the  collar  on 
the  spindle  comes  in  contact  with  the  lower  side  of  the  valve  X.  As  soon  as  water  ap- 
pears at  the  overflow  the  lever  is  drawn  entirely  back  and  the  valve  X  lifted  from  its 
seat,  admitting  a  free  flow  of  steam  through  the  receiving-tube.  Then,  after  closing  the 
overflow- valve  by  rod  L  and  lowering  latch  V  into  teeth  of  ratchet,  the  lever  K  may  be 
pushed  in  to  any  required  point  between  the  stops  on  the  rod  L  so  as  to  obtain  the  de- 
sired water-supply. 

This  instrument  has  a  greater  range  than  the  ordinary  adjustable  injector :  the  mini- 
mum water-supply  is  40  per  cent,  of  the  maximum  supply,  a  larger  quantity  of  water 
is  discharged  by  instruments  of  the  same  size,  and  the  self-adjusting  injector  is  capable 
of  working  with  hotter  water.  Experiments  made  by  the  manufacturers  with  this  in- 
strument gave  the  following  results : 


Pressure  of  steam  in  pounds  per  square  inch  

20 

40 

60 

80 

IOO 

120 

140 

ISO 

Admissible  temperature  of  feed-water  before  enter- 

i?8 

iis 

T  1O 

1  1Q 

132 

T  2  •? 

127 

128 

±OJ 

J  3^ 

*aw 

Aoo 

l*  1 

The  self-adjusting  injector  works  to  the  best  advantage  when  it  is  lifting  water,  and 
in  no  case  must  the  water  be  fed  to  it  under  pressure. 

The  numerical  size  of  an  injector  is  the  diameter  of  the  smallest  part  of  the  delivery- 
tube  expressed  in  millimetres. 

Numerous  modifications  have  been  made  in  the  form  of  injectors  by  different 
makers  with  a  view  to  simplifying  their  construction  and  manipulation  and  extending 
the  range  of  their  action. 

Figure  3,  Plate  XXXV.,  represents  Koerting1  s  universal  lifting -injector,  which 
consists  of  two  injectors  combined  in  the  same  chamber  in  such  a  manner  that  the  de- 
livery-tube of  the  first  injector  communicates  by  means  of  lateral  passages  with  the 
combining- tube  of  the  second  injector.  The  two  steam-valves  V,  V,  and  the  overflow- 
cock  E,  are  connected  with  the  lever  A  in  such  a  manner  that  the  same  movement  of 
this  lever  sets  the  apparatus  in  operation.  By  moving  the  lever  in  the  direction  of  the 


SEC.  15.  BOILER  MOUNTINGS  AND  ATTACHMENTS.  361 

arrow  the  valve  V  is  first  raised  slightly  from  its  seat,  and  as  the  steam  rashes  out 
through  the  open  overflow-cock  E  the  water  is  lifted  and  enters  J.  By  the  continued 
movement  of  the  lever  the  valve  V  is  opened  wide,  and  as  soon  as  the  first  injector  is  in 
operation  its  communication  with  the  overflow  by  means  of  E  is  closed,  and  the  water 
is  forced  into  the  combining-tube  of  the  second  injector.  At  this  moment  the  steam- 
valve  V  of  the  second  injector  begins  to  lift,  and  when  the  second  injector  is  in  full 
operation  its  communication  with  the  overflow  by  means  of  E  is  likewise  closed,  and 
the  water  is  forced  through  the  check-valve  into  the  boiler.  These  several  operations 
take  place  in  such  rapid  succession  that,  practically,  it  is  sufficient  to  raise  the  lever  to 
start  the  apparatus. 

It  is  claimed  that  with  this  injector  water  having  an  initial  temperature  of  156° 
Fahr.  can  be  lifted,  and  that  the  temperature  of  the  water  is  raised  to  190°  Fahr.  in  the 
combining-tube  of  the  first  injector,  the  pressure  produced  in  the  passages  between  the 
first  and  second  injectors  being  considerable,  so  that  the  boiling-point  of  the  water  is 
raised  and  the  condensation  of  a  greater  quantity  of  steam  is  made  possible. 


CHAPTER  XVI. 

TESTS,    INSPECTIONS,  AND   TRIALS   OF  STEAM  BOILEES. 

1.  Testing  Boilers. — All  new  boilers  and  all  boilers  that  have  been  extensively  re- 
paired must  be  subjected  to  a  hydraulic  pressure  in  excess  of  the  highest  working  pres- 
sure, in  order  to  test  the  tightness  of  the  seams  and  rivets,  the  soundness  of  the  plates, 
and  the  structural  strength  of  the  boilers.  Such  tests  must  be  repeated  periodically 
during  the  lifetime  of  the  boiler. 

A  test-pressure  equal  to  three  times  the  working  pressure  was  formerly  held  neces- 
sary by  many  authorities,  but  nowadays  it  is  not  considered  prudent  to  subject  marine 
boilers  of  the  ordinary  form  to  so  severe  a  test.  An  excessive  pressure  may  produce 
injuries  which  do  not  become  apparent  during  the  short  test,  but  which  continue  to 
increase  under  the  ordinary  working  pressure  when  the  boiler  is  put  into  regular  use. 
The  test-pressure  must  in  no  case  strain  any  part  of  the  boiler  beyond  the  limit  of  elas- 
ticity of  the  metal. 

Section  4418  of  the  'Eevised  Statutes  of  the  United  States'  provides  that  "all  boilers 
used  on  steam -vessels,  and  constructed  of  iron  and  steel  plates,  inspected  under  the 
provisions  of  section  4430  (see  section  2,  chapter  v.),  shall  be  subjected  to  a  hydrostatic 
test  in  the  ratio  of  150  Ibs.  to  the  square  inch  to  100  Ibs.  to  the  square  inch  of  the  work- 
ing steam-power  [pressure]  allowed." 

United  States  naval  boilers,  when  new  or  extensively  repaired,  are  also  subjected  to 
a  test-pressure  equal  to  one  and  a  half  times  the  highest  working  pressure  above  the 
atmospheric  pressure. 

French  laws  require  that  tubular  boilers  of  merchant-vessels  are  to  be  tested  to 
double  the  working  pressure  above  the  atmosphere  at  least  once  a  year  and  whenever 
repairs  or  alterations  have  been  made  on  them.  The  boilers  of  French  naval  vessels  are 
subjected,  when  new,  to  a  test-pressure  equal  to  twice  the  working  pressure,  and  annu- 
ally thereafter  to  a  test  of  one  and  a  half  times  the  actual  working  pressure  above  the 
atmosphere ;  but  this  pressure  is  to  be  kept  on  the  boilers  not  longer  than  five  minutes. 
(Ledieu,  '  Traite  des  Appareils  d  Vapeur  de  Navigation,"1  vol.  ii.) 


SEC.  1.  TESTS,  INSPECTIONS,  AND  TRIALS  OF  STEAM  BOILERS.  363 

The  'Steam  Manual,'  issued  by  the  English  Admiralty  (1879),  contains  the  follow- 
ing instructions  regarding  "  Periodical  testing  by  water-pressure  of  the  boilers  of  Her 
Majesty's  ships  and  vessels  in  commission": 

"In  the  case  of  ships  having  new  boilers,  or  boilers  repaired  for  a  commission  of 
four  years,  the  boilers  are  to  be  tested  by  water-pressure  at  the  end  of  two  years' 
service,  and  subsequently  at  half-yearly  intervals  during  the  remainder  of  the 
commission. 

"  As  regards  ships  whose  boilers  have  been  repaired  for  shorter  periods  of  service 
the  boilers  are  to  be  tested  by  water-pressure  at  the  end  of  six  months'  service,  and 
subsequently  at  half-yearly  intervals. 

"During  the  application  of  water-pressure  the  boilers  are  to  be  carefully  examined, 
and  proper  gauges  are  to  be  used  to  detect  any  change  in  the  form  of  the  furnaces, 
combustion-chambers,  etc. 

"The  water-pressure  is  to  be  double  the  working  pressure,  provided  that  during  the 
examination  no  indications  of  weakness  are  observed.  Should,  however,  any  indica- 
tions of  probable  permanent  deformation  be  observed^the  test  is  to  cease,  and  the  work- 
ing pressure  is  then  to  be  limited  to  one-third  that  of  the  test-pressure  arrived  at  before 
such  indications  were  seen. 

"  The  water-pressure  is  intended  to  supplement,  not  to  supersede,  the  occasional 
drill-testing.  Should  the  latter  test  reveal  unusual  thinness  of  any  plates  the  water- 
pressure  is  to  be  very  carefully  applied,  in  order  that  injury  may  not  be  caused  by 
overpressure." 

The  Board  of  Trade  (English)  regulations  for  marine  boilers  provide  as  follows: 
"All  new  boilers,  and  boilers  that  have  been  taken  out  of  ships  for  thorough  repair, 
must  be  tested  by  hydraulic  pressure  up  to  at  least  double  the  working  pressure  that 
will  be  allowed,  previous  to  the  boilers  being  replaced  in  position,  to  test  the  workman- 
ship, etc. ;  but  the  working  pressure  is  to  be  determined  by  the  stay -power,  thickness  of 
plates,  and  strength  of  riveting,  etc." 

Anderson  states  that  the  boilers  belonging  to  the  British  War  Department  are  sub- 
jected periodically,  after  about  every  500  hours  of  actual  work,  to  a  hydraulic  pressure 
equal  to  double  the  pressure  to  which  the  safety-valve  is  ordinarily  loaded,  or  to  one- 
third  of  their  ultimate  strength. 

The  usual  method  of  testing  boilers  is  to  fill  them  with  water  and  produce  a  pres- 
sure within  them  by  means  of  a  hand  force-pump.  All  the  openings  of  the  boiler  are 
securely  closed.  The  safety-valve,  which  is  loaded  to  the  required  test-pressure,  is 
kept  raised  till  the  boiler  is  completely  filled  with  water.  Then,  after  closing  the 


364  STEAM  BOILERS.  CHAP.  XVI. 

safety-valve,  the  pump  is  worked  till  the  steam-gauge  indicates  the  test-pressure.  The 
pump  should  deliver  only  a  small  quantity  of  water  at  each  stroke,  and  must  be  worked 
carefully  as  the  pressure  rises,  in  order  to  avoid  jarring  the  strained  boiler  and  pro- 
ducing a  sudden  rise  of  pressure  beyond  the  limit  of  the  test-pressure.  Some  engineers 
close  the  safety-valve  before  the  boiler  is  quite  full  of  water,  and  so  retain  a  quantity  of 
air  to  act  as  a  cushion  when  the  pressure  is  applied  by  the  pump  ;  but  when  this  en- 
closed air  escapes  through  leaky  seams  and  rivets  no  marks  indicating  such  leaks  are 
left  on  the  plates. 

When  a  boiler  is  connected  with  a  high  steam-drum  the  difference  of  the  pressures 
at  the  top  of  the  steam-drum  and  at  the  bottom  of  the  boiler,  equal  to  the  weight  of  a 
column  of  water  of  corresponding  height,  may  be  a  considerable  quantity.  The  rules 
and  regulations  of  the  Board  of  Supervising  Inspectors  of  Steam -vessels  provide  that, 
"in  applying  the  hydrostatic  test  to  boilers  with  a  steam-chimney,  the  test-gauge  should 
be  applied  to  the  water -line  of  such  boilers." 

The  test  should  be  applied  before  the  boiler  is  painted  and  while  every  part  is  ex- 
posed to  view.  New  boilers  should  be  tested  before  they  leave  the  boiler-shop.  The 
boiler  is  placed  on  blocks  so  that  the  bottom  may  be  inspected,  and  the  furnace  and 
connection  doors  are  kept  wide  open.  Every  part  of  the  boiler  is  watched  and  care- 
fully examined  while  the  pressure  continues,  to  discover  any  leaks  in  rivets,  seams,  or 
tubes,  or  through  cracks  in  the  plates,  and  any  signs  of  bulging  of  stayed  surfaces  or 
of  collapse  of  flues.  Leaky  tubes,  rivets,  and  seams  are  marked,  and  are  calked  after 
the  boiler  has  been  relieved  of  the  pressure.  Flat  stayed  surfaces  and  flues  should  be 
accurately  gauged  before  and  during  the  test. 

"After  the  test-pressure  has  been  maintained  some  time  the  measurements  pre- 
viously obtained  should  be  checked,  and  any  extension,  distortion,  bulging,  etc.,  care- 
fully noted.  Then  again,  when  the  pressure  is  relaxed,  which  may  be  done  suddenly, 
it  should  be  ascertained  whether  any  changes  of  shape  that  may  have  been  found  are 
permanent  or  not.  If  there  be  any  permanent  enlargement  or  distortion,  even  of  the 
slightest  degree,  it  should  be  satisfactorily  examined  to  decide  whether  it  is  due  to  the 
elastic  limit  of  the  material  having  been  exceeded  or  to  malconstruction.  There  are 
cases,  as,  for  instance,  with  flat  surfaces,  where  a  permanent  set  might  take  place,  and 
which  would  be  quite  safe  at  the  ordinary  working  pressure.  This  is  especially  the  case 
with  stayed  surfaces,  for  it  seldom  happens  that  each  stay  in  a  series  takes  its  due  pro- 
portion of  load  until  the  stays  have  been  stretched  or  the  plates  distorted  by  the  pres- 
sure. 

"But  cases  of  a  permanent  flue-tube  distortion  or  flattening  must  always  be  treated 


SEC.  1.  TESTS,  INSPECTIONS,  AND  TRIALS  OP  STEAM  BOILERS.  365 

with  the  greatest  caution,  since  the  change  of  shape  is  liable  to  become  aggravated  on  a 
subsequent  application  of  the  same  or  even  a  less  pressure.  In  all  cases  where  a  perma- 
nent set  is  discovered  the  test  should  be  repeated  again  and  again,  if  necessary,  to  as- 
certain if  the  set  becomes  increased."  ( Wilson.) 

Time  is  an  important  element  in  boiler-tests.  A  boiler  which  bears  a  momentary 
pressure  without  apparent  injury  may  burst  with  the  same  pressure  continued  through 
half  an  hour.  No  boiler  should  be  considered  safe  if  unable  to  bear  the  test-pressure 
for  a  considerable  length  of  time.  The  test-pressure  should  always  be  maintained  at 
least  long  enough  to  enable  the  inspector  to  make  a  thorough  examination  of  all  parts 
of  the  boiler. 

"Want  of  tightness  in  the  joints  is  often  revealed  by  leakage  only  after  the  pres- 
sure has  been  applied  for  some  time.  In  explanation  it  may  be  stated  that  the  steam 
or  water  leaking  from  a  joint  does  not  always  find  its  way  between  the  plates  imme- 
diately opposite  the  point  of  issue,  but  the  actual  source  of  the  leakage,  as  we  may  call 
it,  is  at  some  point  perhaps  several  inches  distant,  whence  it  requires  a  considerable  time 
to  force  its  way  to  the  point  where  it  makes  its  appearance.  There  can  be  no  doubt 
that,  from  the  manner  in  which  boilers  are  usually  put  together,  the  internal  pressure  is 
not  equally  resisted  by  all  parts  of  the  shell,  and  produces  an  undue  and  often  very 
severe  strain  on  one  plate  or  portion  of  a  plate.  This  is  probably  the  cause  of  many 
leakages  that  occur,  and  which  only  '  take  up '  after  the  plate  becomes  stretched  and 
relieved  of  the  extra  strain,  and  it  is,  therefore,  advisable  in  testing  to  allow  the  pres- 
sure to  act  long  enough  to  stretch  such  weak  portions.  .  .  . 

"  It  is  often  much  more  difficult  to  keep  a  boiler  perfectly  tight  and  free  from  oozing 
at  the  rivets,  plate-edges,  stays,  and  tube-ends  under  a  very  high  water-pressure  than 
under  an  equal  pressure  of  steam.  This  is  probably  owing  to  the  fact  that  the  high 
temperature  in  the  latter  case  tends  to  close  the  joints,  and  with  certain  kinds  of  water 
any  slight  oozing  is  found  to  take  up  by  the  opening  becoming  closed  with  deposit  or 
corrosion  which  is  induced  by  the  high  temperature."  (  Wilson.) 

Cold  water  is  generally  used  in  testing  boilers.  Some  engineers  advocate  the  use  of 
hot  water,  because  the  expansion  of  the  metal  due  to  the  higher  temperature  brings  the 
different  parts  of  the  boiler  more  nearly  under  the  conditions  of  stress  which  obtain 
when  the  boiler  is  in  actual  use,  and  because  at  low  temperatures  iron  is  more  easily 
injured  by  strains.  The  water  should,  however,  not  be  so  hot  as  to  be  liable  to  cause 
injury  by  scalding  in  case  of  serious  leaks,  or  to  interfere  with  a  thorough  examination 
of  the  boiler  within  the  furnaces  and  connections  as  well  as  outside.  The  effects  pro- 
duced by  the  uniform  expansion  of  the  whole  boiler  when  hot  water  is  used  are,  how- 


366  STEAM  BOILERS.  CHAP.  XVI. 

ever,  very  unlike  the  effects  produced  by  the  local  expansion  of  the  parts  in  immediate 
contact  with  the  fire  and  hot  gases. 

Boilers  have  been  tested  by  filling  them  completely  with  water  and  lighting  a  fire  in 
the  furnaces,  the  pressure  being  produced  by  the  expansion  of  the  water.  (See  Specifi- 
cations of  Boilers  of  U.  S.  S.  Miantonomoh  and  class,  section  10,  chapter  vii.)  It 
is  claimed  that  with  this  method  the  increase  of  pressure  is  much  more  gradual  than 
that  produced  by  a  pump,  and  that  the  conditions  of  actual  practice,  as  far  as  diffe- 
rences of  temperature  are  concerned,  are  at  least  approximately  obtained.  But  a  care- 
ful examination  of  the  furnaces  and  back-connections  is  not  possible  with  this 
method. 

According  to  Wilson,  it  is  not  an  unfrequent  practice  in  England  to  test  new  boil- 
ers by  steam  under  a  pressure  one  and  a  quarter  or  one  and  a  half  times  greater  than 
the  working  pressure.  It  is  argued  that  this  is  the  only  method  by  which  the  same 
conditions  of  strain  can  be  produced  as  obtain  when  the  boiler  is  worked.  But  this 
practice  is  to  be  condemned,  not  only  because  it  is  dangerous,  but  because  it  renders  a 
careful  examination  of  the  furnaces  and  back-connections,  while  the  pressure  lasts,  im- 
possible. 

Boilers  that  have  been  tested  with  water-pressure  should  be  tested  under  steam  to 
their  working  pressure,  in  order  to  prove  their  tightness  after  they  have  been  located 
and  connected  in  the  vessel,  and  before  their  shell  has  been  covered  with  felt  or  other 
non-conductive  material.  Every  leaky  seam,  rivet,  or  tube  should  be  made  tight  before 
the  boiler  is  finally  accepted  for  service. 

2.  Inspection  of  Boilers. — The  testing  of  boilers  by  hydraulic  pressure  has  to  be 
regarded  merely  as  an  auxiliary  means  for  ascertaining  the  strength  and  workmanship 
of  a  boiler ;  it  should  never  be  considered  as  making  a  careful  examination  of  every 
accessible  part  unnecessary.  Boilers  which  are  faulty  in  design,  or  built  of  inferior 
material,  or  have  bad  workmanship  put  on  them  may  stand  the  hydraulic  test,  but, 
under  the  varying  and  continued  strains  of  actual  practice,  they  will  sooner  or  later 
develop  weaknesses  which  seriously  impair  their  life  and  safety.  Grave  defects  may 
be  hidden  from  view  after  a  boiler  is  built  so  that  they  cannot  be  discovered  by 
the  closest  scrutiny ;  therefore  the  inspection  of  boilers  should  commence  with  the 
process  of  construction,  and  should  be  repeated  frequently  during  the  lifetime  of  the 
boiler. 

Section  4418  of  the  'Revised  Statutes-  of  the  United  States'  provides  that  "the  local 
inspectors  shall  inspect  the  boilers  of  all  steam- vessels  before  the  same  shall  be  used, 
and  once  at  least  in  every  year  thereafter.  They  shall  subject  aD  boilers  to  the 


SBC.  8.  TESTS,  INSPECTIONS,  AND  TRIALS  OF  STEAM  BOILERS.  367 

hydrostatic  pressure,  and  shall  satisfy  themselves  by  thorough  examination  that  the 
boilers  are  well  made,  of  good  and  suitable  material,  etc." 

The  regulations  of  the  Board  of  Trade  (English)  for  the  survey  of  marine  boilers  pro- 
vide that,  when  a  boiler  is  not  open  to  inspection  during  the  whole  period  of  its  con- 
struction, the  factor  of  safety  for  cylindrical  boilers  is  to  be  increased  27.5  per  cent,  (see 
section  3,  chapter  ix.) ;  that  special  attention  should  be  paid  to  the  survey  of  super- 
heaters, which  must  be  inspected  inside  and  out ;  that  the  hammer-test  should  not 
be  relied  on  entirely  for  superheaters,  but  that  the  plates  should  be  drilled  occa- 
sionally. 

When  boilers  for  United  States  naval  vessels  are  built  under  contract  at  private 
establishments  inspecting  engineer  officers  are  detailed  to  watch  their  construction,  and 
to  see  that  they  are  built  in  strict  conformity  to  the  drawings,  and  that  the  mate- 
rial and  workmanship  are  of  the  best  quality 'and  in  accordance  with  the  speci- 
fications. 

The  attention  of  inspecting  officers  is  to  be  directed  especially  to  the  following 
points : 

All  the  material  must  be  of  the  proper  quality,  without  flaws,  and  of  the  prescribed 
dimensions.  It  is  not  an  uncommon  practice  with  boilermakers  to  use  plate-iron  of  an 
inferior  quality  for  the  internal  parts  of  a  boiler,  which  are  hidden  from  view  when  the 
boiler  is  finished. 

Flanged  plates  must  show  no  cracks  or  signs  of  laminations.  Cracks  extending  from 
punched  holes  to  the  edge  of  the  plate,  or  from  hole  to  hole,  are  dangerous  sources  of 
weakness,  and  frequently  indicate  an  inferior  iron.  Cracks  are  often  produced  in  a  row 
of  rivets  by  drifting. 

When  the  rivet-holes  in  a  seam  do  not  come  fair  they  should  not  be  corrected  by 
drifting ;  nor  is  the  use  of  smaller  rivets  in  half-blind  holes  to  be  permitted.  When  the 
half -blind  holes  of  a  seam  are  corrected  by  punching  or  drilling  so  much  of  the  metal 
may  be  cut  away  that  the  strength  of  the  joint  is  seriously  impaired,  or  that  the  holes 
can  be  closed  only  imperfectly  by  the  rivets. 

All  plates  drilled  in  place  must  be  taken  apart,  and  the  burr  must  be  removed  from 
all  drilled  holes. 

When  plates  are  cut  too  small  the  boilermaker  often  tries  to  correct  the  mistake  by 
punching  the  holes  of  the  seams  closer  to  the  edge  of  the  plates.  All  laps  must  be  of 
the  proper  width,  and  the  joints  of  contiguous  plates  must  be  placed  as  far  as  possible 
apart. 

When  the  laps  of  plates  do  not  lie  close  together  the  boilermaker  often  tries  to  cor- 


368  STEAM  BOILERS.  CHAP.  XVL 

rect  or  hide  the  evil  by  excessive  calking,  or  by  the  insertion  of  pieces  of  hoop-iron,  or 
by  filling  the  open  space  with  cement  of  cast-iron  borings  mixed  with  sal-ammoniac. 
By  these  means  the  bad  workmanship  may  be  concealed  during  the  cold-water  test,  but 
it  will  cause  trouble  sooner  or  later  under  steam. 

The  edges  of  all  plates  should  be  planed  or  chipped  fair  before  calking. 

See  that  the  proper  width  of  water-spaces  is  maintained  between  the  shell  of  the 
boiler  and  the  back-connections,  and  that  there  is  sufficient  clearance  between  the 
flanges  or  strengthening-hoops  of  cylindrical  furnace-flues  and  adjoining  parts. 

The  tube-holes  must  be  bored  of  such  a  size  that  the  tubes  fit  them  exactly.  The 
tube-ends  must  not  be  expanded  excessively,  and  must  show  no  cracks  after  being 
expanded.  The  tube-ends  should  project  at  least  £  inch  beyond  the  tube-plates. 

In  the  boilers  built  by  contract  for  a  United  States  naval  vessel  several  tubes  had 
been  cut  too  short.  To  hide  this  defect  short  pieces  of  tube,  turned  down  to  a  thin 
edge  at  one  end,  had  been  inserted  in  the  back  end  of  these  tubes  ;  the  tubes  and  fer- 
rules had  then  been  expanded  together  and  the  projecting  end  of  the  ferrules  beaded 
over.  This  work  was  so  neatly  done  that  the  piecing  of  the  tubes  could  not  be  detected 
by  the  eye,  and  the  tubes  showed  no  leaks  under  the  cold-water  pressure,  but  the 
continued  leaking  of  the  tubes  under  steam  led  to  the  discovery  of  their  dangerous 
condition. 

In  the  same  boilers  the  pin-holes  in  the  T-ends  of  several  braces  did  not  come  fair 
with  the  holes  in  the  angle-irons  riveted  to  the  shell  of  the  boilers.  Smaller  bolts  had 
been  used  to  connect  the  braces  to  the  angle-irons,  and  several  bolts  had  been  omitted 
entirely. 

The  bolts  or  pins  of  braces  must  fit  the  holes  exactly,  and  must  be  secured  by  nuts 
or  cotters.  The  T  or  angle  irons  to  which  the  braces  are  attached  must  be  securely 
riveted  to  the  shell.  Their  rivet-holes  must  show  no  cracks,  and  their  bolt-holes  must 
not  come  too  close  to  the  edge  of  the  flange.  The  long  braces  must  be  of  equal  tension  ; 
they  must  be  straight,  not  bent  to  clear  anything.  Examine  especially  the  stays  run- 
ning across  the  boiler  between  horizontal  tubes  to  see  that  there  is  no  danger  of  their 
bearing  against  the  tubes.  The  holes  of  stay-bolts  must  come  exactly  opposite  each 
other  in  both  plates. 

The  explosion  of  the  boiler  of  the  TL  S.  S.  Chenango,  in  1864,  was  due  to  the  omis- 
sion of  several  braces. 

See  that  no  pieces  of  wood  or  iron  have  been  left  inside  the  boiler  under  and  between 
the  furnaces ;  that  the  valves  open  and  close  freely ;  that  no  pipes  are  closed  by 
blank  flanges  ;  that  the  gauge-pipes  are  not  closed  by  putty  or  rubber  packing. 


SEC.  3.  TESTS,  INSPECTIONS,  AND  TRIALS  OP  STEAM  BOILERS.  369 

After  the  hydraulic  test  the  boiler  should  always  be  examined  inside  to  see  whether 
the  braces  or  their  fastenings  show  any  signs  of  having  been  unduly  strained. 

The  periodical  examination  of  boilers  which  have  been  in  use  is  directed  to  the  dis- 
covery of  leaky  tubes,  seams,  rivets,  and  stay-bolts  ;  of  cracks  and  blisters,  and  of  the 
distortion  of  plates  by  overheating  ;  of  the  accumulation  of  scale  between  the  tubes  and 
on  the  furnace-crowns,  and  of  loose  scale  and  dirt  in  the  water-bottoms.  The  extent  of 
coiTosion  of  rivet-heads,  of  braces  and  their  fastenings,  and  of  plates  must  be  carefully 
investigated. 

The  hammer -test  is  much  relied  on  in  examining  old  boilers.  The  plates  are  tapped 
lightly  with  a  hand-hammer,  and  from  the  sound  given  out  and  the  rebound  of  the  ham- 
mer conclusions  are  drawn  as  to  the  thickness  and  soundness  of  the  plates.  In  making 
this  test  the  influence  of  the  more  or  less  close  proximity  of  stays,  angle-irons,  or  gusset- 
plates  on  the  vibrations  and  springiness  of  plates  must  be  taken  into  consideration. 

When  the  thickness  of  plates  appears  doubtful  a  small  hole  is  drilled  through 
them. 

3.  Trials  of  Boilers. — Experiments  on  the  evaporative  power  of  boilers  are,  in 
general,  of  two  kinds,  being  designed  to  determine  either  the  greatest  weight  of  water 
which  the  boilers  are  capable  of  evaporating  in  a  unit  of  time,  or  the  weight  of  fuel  re- 
quired for  the  evaporation  of  a  given  weight  of  water. 

Numerous  experiments,  made  under  the  direction  of  the  Bureau  of  Steam-engineer- 
ing of  the  United  States  Navy  Department,  to  determine  the  relative  evaporative  effi- 
ciency of  different  types  of  boilers  ;  the  influence  of  changes  in  the  proportions  of  grate- 
surface,  heating-surface,  and  calorimeter,  and  in  the  rate  of  combustion,  on  the  evapora- 
tive efficiency  of  boilers  ;  and  the  value  of  different  kinds  of  fuel  for  marine  boilers,  have 
been  described  by  Isherwood  in  '  Experimental  Kesearches '  and  in  the  various  reports 
submitted  by  the  boards  of  United  States  naval  engineers  charged  with  the  conduct  of 
these  experiments. 

In  all  such  experiments  the  quantity  of  water  fed  into  the  boiler,  the  weight  of  fuel 
actually  burnt  and  the  weight  of  refuse  matter  of  the  fuel  remaining  unconsumed,  the 
pressures  of  steam  and  of  the  outside  air,  and  the  temperatures  of  the  feed- water,  steam, 
external  air,  and  chimney -gases  should  be  carefully  measured  with  accurately -tested 
instruments,  and  the  observations  noted  at  regular  intervals.  The  firing  must  be  done 
by  experienced  men  and  in  a  uniform  manner.  The  fuel  must  be  of  a  known  and  uni- 
form quality.  All  conditions  affecting  combustion  and  evaporation  in  any  manner  must 
be  carefully  recorded.  Foaming  must  be  guarded  against.  To  prevent  leakage  of  steam 
or  water  the  boiler  must  be  tested  under  steam  and  water  pressures  before  the  experi- 


370  STEAM  BOILERS.  CHAP.  XVI. 

ment  commences,  and  the  boiler  itself  and  the  joints  of  all  its  pipes  and  valves  must  be 
made  perfectly  tight. 

Sometimes  the  steam  generated  in  a  boiler  experiment  is  utilized  in  working  an  en- 
gine, and  the  weight  of  water  evaporated  is  deduced  from  indicator  diagrams  taken  at 
intervals  during  the  trial.  This  method  gives,  however,  no  reliable  results,  since  the 
loss  of  steam  by  condensation  and  leakage  in  the  cylinders,  valves,  and  pipes  varies 
greatly  under  different  conditions  of  the  mechanism  and  with  the  manner  of  work- 
ing the  engines. 

Errors  resulting  from  leakage,  foaming,  and  radiation  will  generally  be  diminished 
by  evaporating  the  water  under  atmospheric  pressure. 

The  longer  the  time  during  which  the  experiment  is  continued,  the  less  is  the  final 
result  affected  by  accidental  disturbing  elements  and  by  inaccuracies  of  measurement 
and  errors  of  observation. 

Each  boiler  experiment  conducted  under  the  direction  of  the  Bureau  of  Steam- 
engineering  lasts,  if  possible,  from  24  to  72  consecutive  hours.  The  shorter  the  duration 
of  the  experiment,  the  shorter  should  be  the  intervals  of  time  between  the  recorded 
observations. 

For  the  sake  of  comparison  the  resiilts  of  experiments  on  the  evaporative  efficiency 
of  boilers  are  to  be  reduced  to  a  uniform  standard.  For  this  piirpose  it  is  convenient  to 
calculate  the  weight  of  water  of  a  fixed  temperature  (either  100°  or  212°  Fahr.)  which 
would  be  evaporated  under  a  fixed  barometrical  pressure  of  the  atmosphere,  provided 
the  same  number  of  units  of  heat  were  communicated  to  the  water  under  these  condi- 
tions as  were  transmitted  to  the  water  in  the  boiler  per  pound  of  fuel,  or  of  combus- 
tible matter  of  the  fuel,  consumed  per  hour. 

The  following  extract  from  the  'Report  on  the  Murphy  Grate-bar,'  by  a  board  of 
United  States  naval  engineers,  June  25,  1878,  gives  a  description  of  the  usual  method 
pursued  in  making  the  numerous  boiler  experiments  which  have  been  carried  on  under 
the  direction  of  the  Bureau  of  Steam-engineering : 

"  Before  commencing  the  experiments  the  blow-off  pipe  was  removed  and  a  plate 
bolted  across  the  aperture.  This  pipe  was  the  only  means  through  which  water  could 
escape  from  the  boiler.  A  temporary  steam-escape  pipe  of  1\  inches  inside  diameter 
was  bolted  on  the  top  of  the  steam-drum,  giving  a  straight  discharge  to  the  steam.  The 
safety-valve,  of  5  inches  diameter,  was  removed  from  its  chamber,  and  the  permanent 
escape-pipe  attached  to  it  was  used  in  addition  to  the  temporary  escape-pipe.  .  .  . 

"  The  feed- water,  previous  to  entering  the  boiler,  was  accurately  measured  in  two 
covered  tanks  placed  on  the  hurricane  or  upper  deck  of  the  vessel.  One  of  these  tanks 


SBC.  3.  TESTS,  INSPECTIONS,  AND  TRIALS  OF  STEAM  B01LEES.  371 

discharged,  by  measurement,  54.67535  cubic  feet  of  water,  and  the  other  discharged 
47.59028  cubic  feet  of  water  at  each  delivery.  The  two  tanks  were  connected  by  a  pipe 
at  their  bottom,  and  in  this  pipe  were  two  stop-cocks,  one  at  each  tank.  From  the 
centre  of  the  pipe  connecting  the  tanks  another  pipe  was  carried  vertically  downward 
15  feet  to  the  check- valve  near  the  bottom  of  the  boiler,  so  that  the  feeding  of  the  boiler 
was  effected  by  gravity,  the  quantity  of  water  entering  being  regulated  by  the  stop- 
cocks in  the  connecting-pipe.  The  tanks  were  supplied  with  lake-water  by  a  small 
steam-pump  worked  with  steam  from  a  donkey-boiler. 

"All  the  coal  consumed  was  carefully  weighed  on  a  tested  platform-scales  in  quan- 
tities of  182  pounds  at  each  weighing.  The  refuse  from  this  coal  in  ash,  clinker,  soot, 
etc.,  was  similarly  weighed  and  in  the  dry  state. 

"At  the  end  of  each  experiment  the  furnaces,  smoke-connections,  flues,  and  tubes 
were  swept  clean  of  soot  and  ash,  which  were  weighed,  and  their  weight  added  to  that 
of  the  refuse  withdrawn  from  the  furnaces  and  ashpits. 

"  In  commencing  an  experiment  the  water  in  the  boiler  was  brought  to  the  boiling- 
point  under  the  atmospheric  pressure  by  wood  alone,  which  was  then  allowed  to  burn 
down  to  the  embers  required  for  igniting  the  coal.  No  account  was  taken  of  the  weight 
of  wood  thus  consumed.  The  water-level  in  the  boiler  was  now  adjusted  to  the  proper 
height  in  the  glass  water-gauge,  the  time  noted,  the  coal  fired,  and  the  experiment  held 
to  commence.  Each  experiment  was  ended  with  the  water  in  the  boiler  at  the  same 
level  as  at  the  commencement,  and  with  the  fires  entirely  burned  out.  It  was  intended 
that  each  experiment  should  last  twenty -four  consecutive  hours,  and  from  this  duration 
none  varied  more  than  a  few  minutes.  .  .  . 

"  One  machinist  was  stationed  at  the  tanks  to  note  the  time  each  was  discharged  and 
to  report  it  to  the  engineer  of  the  watch.  Another  was  stationed  in  the  fire-room  to  see 
the  firing  properly  performed.  A  third  was  stationed  at  the  scales  for  weighing  the  coal 
and  its  refuse.  The  watches  were  four  in  number,  of  six  hours'  duration  each,  and  were 
superintended  by  the  members  of  the  board  and  the  two  engineer  officers  of  the  Michi- 
gan, who  personally  weighed  the  coal  and  its  refuse,  and  kept  a  log,  or  tabular  record, 
in  the  columns  of  which  were  entered  hourly  the  kind  of  breeze  blowing,  the  height  of 
the  barometer,  the  steam-pressure  in  the  boiler,  the  pounds  of  coal  thrown  into  the  fur- 
naces, the  pounds  of  refuse  in  ash,  clinker,  etc.,  withdrawn  from  the  furnaces  and  ash- 
pits, the  temperature  of  the  air  on  deck  and  in  the  fire-room,  the  temperature  of  the 
feed-water  in  the  tanks,  and  the  temperature  of  the  gases  of  combustion  in  the  chimney. 
This  last  temperature  was  obtained  by  means  of  a  metallic  pyrometer  placed  perma- 
nently in  the  base  of  the  chimney,  with  its  index  outside." 


372  STEAM  BOILERS.  CHAP.  XVI. 

The  following  description  of  an  approximate  method  for  determining  the  tempera- 
tures of  the  gases  in  the  uptake  of  a  boiler  is  taken  from  the  '  Report  on  the  Ashcroft 
Furnace-doors  and  Grate-bars,'  by  a  board  of  United  States  naval  engineers,  March  27, 
1878: 

"  The  best  approximation  to  the  temperature  of  the  gases  of  combustion  in  the  boiler- 
uptakes  that  could  be  made  was  to  place  on  little  wire  tripods  small  fragments  of  tin, 
lead,  zinc,  and  antimony,  and  then  insert  these  tripods  into  the  mouths  of  the  tubes  at 
their  uptake  ends  ;  the  pieces  of  metal  being  at  about  the  axes  of  the  tubes  and  wholly 
surrounded  by  the  escaping  hot  gases  of  combustion,  the  tripods  touching  the  tubes  at 
only  three  points.  The  melting-points  of  these  metals  may  be  taken  approximately  at 
450°,  650°,  750°,  and  850°  Fahr.  ;  and  it  is  obvious  that  if  one  of  them  were  found 
melted,  and  the  next  not  melted,  the  temperature  of  the  gases  of  combustion  passing 
over  them  must  have  been  somewhere  between  the  respective  melting-points.  In  this 
manner  two  limits  of  temperature  are  found  at  about  200°  Fahr.  apart,  as  an  extreme,  the 
mean  perhaps  not  varying  too  widely  from  the  truth  for  practical  purposes.  Three  tri- 
pods were  placed  in  the  top  row  of  tubes,  three  in  the  middle,  and  three  in  the  bottom  row 
of  the  tubes  of  each  furnace — one  tripod  in  the  next  to  the  corner  tubes  of  each  of  these 
rows,  and  the  third  in  the  middle  tube  of  the  row  ;  but  the  mean  of  all  the  approximate 
temperatures  thus  found  cannot  be  assumed  as  the  mean  temperature  of  the  whole  mass 
of  escaping  gas,  because  the  velocity  of  this  gas  varies  much  through  the  different  tubes, 
being  greatest  through  the  top  row,  least  through  the  bottom  row,  and  intermediate 
in  the  rows  between.  The  melting-points  of  the  metals,  though  they  furnish  only  indi- 
cations of  the  temperature,  prove  the  enormous  difference  in  the  temperature  of  the 
gases  of  combustion  escaping  from  the  top  and  bottom  rows  of  tubes  separated  by  a 
vertical  distance  of  but  a  few  inches — a  difference  sometimes  as  great  as  300°  Fahr." 

To  eliminate  the  errors  due  to  inaccuracies  in  observing  the  steam-pressure,  to  super- 
heating of  the  steam,  and  to  the  presence  of  Tinvaporized  water  in  the  steam  escaping 
from  the  boiler,  the  whole  of  this  steam  may  be  led  to  a  surface-condenser,  the  weights 
and  temperatures  of  the  water  of  condensation  and  of  the  condensing  water  before  enter- 
ing and  after  leaving  the  condenser  measured,  and,  from  these  data,  the  units  of  heat 
actually  present  in  the  steam  may  be  calculated.  This  method  was  used  in  the  trials 
of  steam  boilers  at  the  Fair  of  the  American  Institute  in  1871. 

In  other  instances  the  quality  of  the  steam  has  been  determined  at  regular  intervals 
during  the  trial  by  introducing  a  portion  of  the  steam  into  a  calorimeter,  where  it  was 
employed  to  heat  a  known  quantity  of  water.  This  method  was  used  in  the  boiler-tests 
at  the  International  Exhibition,  Philadelphia,  1876.  A  tank  containing  a  known 


Sic.  3.  TESTS,  INSPECTIONS,  AND  TRIALS  OP  STEAM  BOILERS.  373 

weight  of  water  of  a  known  temperature  was  set  on  scales.  Into  this  a  sufficient  quan- 
tity of  steam  was  admitted  to  raise  the  temperature  of  the  water  a  certain  number  of 
degrees.  From  the  differences  of  the  weights  and  temperatures  of  the  water  in  the  tank 
before  and  after  the  admission  of  steam  the  number  of  units  of  heat  in,  and  the  weight 
of,  the  steam  were  found. 


CHAPTER  XYII. 

MANAGEMENT  OF  BOILERS. 

1.  Getting  up  Steam. — When  the  order  is  given  to  get  up  steam  commence 
closing  the  boilers  as  soon  as  possible,  so  that,  in  case  the  joints  of  the  manhole  or 
handhole  plates  should  be  found  to  leak  after  the  water  is  run  up  in  the  boiler,  the 
latter  can  be  emptied  and  the  joints  remade  without  delaying  the  starting  of  the  fires. 
Before  closing  the  boiler  satisfy  yourself  that  all  the  braces  are  secured,  and  that  no 
articles  used  in  repairing  or  cleaning  the  boiler  have  been  left  inside. 

Rubber  gaskets,  manufactured  in  continuous  rings  of  the  size  and  shape  required, 
are  used  almost  universally  for  making  the  joints  of  manhole  and  handhole  plates. 
When  gaskets  are  cut  out  of  sheet-rubber  they  are  generally  made  in  several  pieces 
with  dovetailed  ends,  in  order  to  economize  material.  The  gasket  must  fit  accurately 
around  the  projecting  rim  of  the  plate  and  lie  perfectly  flat  on  the  flange.  When  the 
flange  of  the  plate,  and  the  ring  around  the  manhole  on  which  it  seats,  are  smooth  and 
level  the  joint  can  be  made  tight  without  using  white  or  red  lead,  which  makes  the  rub- 
ber hard  and  brittle.  In  removing  the  plate  the  rubber  gasket  is  apt  to  stick  partly  to 
the  boiler  and  partly  to  the  plate,  and  thus  become  injured.  This  may  be  prevented  by 
coating  the  gasket  with  black  lead  on  the  side  in  contact  with  the  boiler.  A  mixture  of 
black  lead  and  tallow  is  also  used  for  this  purpose  and  to  soften  the  gasket,  but  the  tal- 
low rots  the  rubber.  A  coating  of  white  lead  is  frequently  put  on  the  flange  of  the 
plate,  so  that  the  gasket  may  stick  to  the  plate  in  preference  to  sticking  to  the  boiler. 
When  a  manhole-plate  is  found  to  leak  after  steam  has  been  raised  it  may  often  be 
made  tight  by  driving  thin,  flat  wedges  of  soft  pine  wood  between  the  projecting  rim  of 
the  plate  and  the  edge  of  the  manhole.  The  sides  of  these  wedges  should  be  slightly 
bevelled,  and  adjoining  wedges  should  overlap  one  another. 

All  the  valves  and  cocks  connected  with  the  boiler  should  be  examined  before 
getting  up  steam,  to  make  sure  that  they  can  be  operated  freely.  The  steam  stop- 
valves  are  closed,  but  it  is  well  to  ease  them  off  their  seat  slightly,  else  it  may  happen 
that,  in  consequence  of  the  uneqiial  expansion  of  the  valve-disc  and  chamber  when 
steam  first  begins  to  form,  the  valve  be  jammed  in  its  seat.  The  safety-valves  are 

374 


SEC.  1.  MANAGEMENT  OP  BOILERS.  375 

raised  and  kept  open  till  steam  begins  to  form,  to  allow  the  escape  of  air  from  the 
boiler. 

The  boilers  are  filled  either  by  opening  the  bottom  blow- valves  and  letting  the  water 
run  in  from  the  sea,  or  by  pumping  water  in  through  the  check-valves.  When  the  water 
is  taken  from  a  tank  or  hydrant  on  shore  it  may  be  run  in  by  means  of  a  hose  through  a 
manhole  on  top  of  the  boiler  or  through  the  safety-valve.  Boilers  should  be  filled  with 
warm  water  when  practicable.  The  height  of  the  water  within  the  boiler  before  it  has 
risen  to  the  level  of  the  water-gauges  may  be  found,  when  the  temperature  of  the 
entering  water  is  different  from  that  of  the  boiler-shell,  by  applying  the  hand  to  the 
shell  and  judging  by  the  feeling.  Or  it  may  be  found  by  tapping  the  shell  with  a  ham- 
mer and  judging  by  the  different  sounds  produced  at  places  where  the  boiler  is  filled 
and  empty.  To  know  whether  the  water  is  rising  in  the  boiler  when  it  enters  through 
the  bottom  blow-valve,  open  the  water-gauge  cocks  and  apply  the  hand  or  a  lighted 
lamp  to  the  opening  ;  the  rising  water  will  expel  the  air  through  the  opening. 

Before  charging  the  furnaces  with  fuel  see  that  the  grates,  bridge-walls,  and  ashpits 
are  quite  clear  of  ashes,  clinker,  etc.,  that  the  tubes  are  unobstructed,  and  that  no  arti- 
cles are  left  in  the  front  or  back  connections.  Then  close  the  uptake-doors.  Remove 
the  hood  from  the  chimney  and  open  the  damper.  Hoist  the  chimney  and  secure  it. 
Leave  the  stays  slack,  and  defer  their  adjustment  till  after  the  fires  are  well  started  and 
the  pipe  has  become  hot ;  but  never  set  them  up  quite  rigid. 

In  charging  the  furnaces  the  back  of  the  grate  is  covered  evenly  with  a  thin  layer  of 
small  coal ;  on  the  front  of  the  grate  some  billets  of  split  wood  are  placed  side  by  side, 
the  ends  of  which  are  supported  by  a  couple  of  pieces  laid  crosswise  the  furnace.  A 
few  shovelfuls  of  coal  are  thrown  on  the  wood,  and  some  small  kindling-wood,  shav- 
ings, oily  rags,  or  other  inflammable  substances  are  placed  at  the  furnace-mouth  below 
the  layer  of  wood. 

When  the  water  has  risen  to  the  proper  height  in  the  boiler  the  kindling-wood  in 
the  furnaces  is  lighted  ;  the  furnace-doors  are  kept  slightly  open  and  the  ashpit-doors 
partly  closed  till  the  whole  mass  of  wood  has  caught  fire.  More  coal,  broken  up  in 
small  pieces,  is  thrown  on  the  burning  mass,  and  the  furnace-doors  are  closed  and  the 
ashpit-doors  opened.  When  the  heap  of  coal  on  the  front  of  the  grate  has  become  in- 
candescent it  is  partly  pushed  back ;  more  coal  is  added,  which  is  likewise  pushed 
gently  back  as  soon  as  it  becomes  incandescent.  This  operation  is  repeated  till  there  is 
a  sufficient  mass  of  burning  coal  on  the  grate. 

Sometimes,  especially  in  very  damp  weather  or  when  the  air  meets  with  many  ob- 
structions in  flowing  to  the  ashpits,  it  may  be  necessary  to  produce  an  artificial  draught 


376  STEAM  BOILERS.  CHAP.  XVII. 

in  the  chimney  in  order  to  start  the  fires.  By  placing  some  burning  shavings  in  the 
uptake,  and  then  closing  the  uptake-doors  quickly,  the  column  of  air  in  the  chimney  is 
heated  and  an  ascending  current  is  produced. 

When  it  is  necessary  to  raise  steam  with  all  possible  despatch  for  a  great  emergency 
the  fires  may  be  lighted  while  the  water  is  still  rising  in  the  boiler,  as  soon  as  the  heat- 
ing-surfaces are  barely  covered  with  water?  and  the  water  is  then  allowed  to  rise  only  to  its 
lowest  admissible  level  in  the  gauge-glass.  By  using  bituminous  coal  or  greasy  or  tarry 
matter  in  starting  the  fires  the  time  required  for  getting  up  steam  may  be  greatly  short- 
ened. By  this  means  steam  may  be  raised  from  cold  water  in  large  marine  boilers  in  a 
comparatively  short  time.  The  unequal  expansion  of  the  parts  in  contact  with  the  fire 
and  the  products  of  combustion,  and  of  the  boiler-shell,  causes  very  injurious  strains, 
especially  when  the  fires  are  urged  from  the  beginning  while  the  water  is  still  cold, 
which  should,  therefore,  be  avoided  except  in  cases  of  great  emergency.  The  fires 
should  be  allowed  to  burn  up  slowly  by  being  kept  banked  while  the  water  is  being 
heated.  Under  ordinary  circumstances  not  less  than  three  hours  should  be  allowed  for 
getting  up  steam.  With  very  long  cylindrical  boilers,  like  the  double-end  boiler  repre- 
sented on  Plate  XV.,  it  is  advisable  to  allow  even  six  hours  for  this  purpose. 

A  great  saving  of  wood  may  be  effected,  when  there  is  no  hurry  in  getting  up  steam, 
by  starting  fires  with  wood  at  first  only  in  the  alternate  furnaces  of  the  boiler,  and  then 
transferring  some  of  the  incandescent  coal  to  the  other  furnaces,  the  grates  of  which 
have  been  previously  covered  with  a  thin  layer  of  coal. 

As  soon  as  a  light  column  of  steam  rises  from  the  escape-pipe  or  issues  from  the 
open  gauge-cocks  the  safety-valves  are  closed,  the  stop- valves  opened,  and  the  boilers 
put  in  communication  with  each  other. 

2.  Firing. — The  thickness  of  the  bed  of  fuel  on  the  grate  must  be  regulated,  accord- 
ing to  the  kind,  quality,  and  size  of  the  fuel  and  to  the  force  of  the  draught,  in  such  a 
manner  as  to  ensure  the  passage  of  the  proper  quantity  of  air  evenly  distributed  through 
the  grate. 

With  ordinary  chimney-draught,  giving  a  rate  of  combustion  of  from  12  to  16  Ibs. 
of  coal  per  square  foot  of  grate  per  hour,  a  fire  of  anthracite  coal  of  egg-size  may  be 
carried  from  5  to  6  inches  thick.  A  thin  fire,  under  otherwise  equal  conditions,  offers 
less  resistance  to  the  passage  of  the  air  through  the  grate,  and  is  thus  favorable  to  a 
rapid  rate  of  combustion.  When  the  lumps  of  coal  are  of  smaller  size  the  fire  may  be 
carried  relatively  thinner  ;  but  when  the  fire  is  less  than  four  inches  thick  a  large  grate 
cannot  be  kept  evenly  covered,  and  too  much  air  will  pass  through  the  grate.  When 
bituminous  coal  is  used  with  a  rapid  rate  of  combustion  the  fire  must  be  carried  thicker 


SEC.  2.  MANAGEMENT  OP  BOILERS.  377 

than  with  anthracite  coal,  else  the  grate  cannot  be  kept  covered  evenly  ;  this  is  espe- 
cially the  case  with  free-burning  semi-bituminous  coals. 

With  a  forced  draught  the  thickness  of  the  fire  is  to  be  increased,  and  the  size  of  the 
lumps  of  anthracite  coal  should  be  diminished  at  the  same  time. 

The  furnaces  should  be  fired  regularly  with  moderate  charges.  When  much  coal  is 
thrown  into  the  furnace  it  will  take  a  long  time  to  kindle  ;  but  when  the  charges  are 
very  small  and  oft  repeated  the  frequent  opening  of  the  door  causes  a  waste  of  heat. 
Anthracite  coal  may  be  fired  at  intervals  of  from  15  to  20  minutes,  according  to  the  rate 
of  combustion.  Bituminous  coal,  especially  when  it  is  of  small  size,  should  be  fired 
more  frequently,  every  10  or  15  minutes,  because  the  evolution  of  the  hydrocarbon 
gases  as  each  charge  is  thrown  into  the  furnace  makes  a  large  quantity  of  heat  latent, 
and  the  temperature  of  the  furnace  would  vary  greatly  if  a  large  mass  of  coal  was  in- 
troduced into  the  furnace  at  one  time.  Each  charge  of  coal  should  be  spread  in  an  even 
layer  over  the  grate,  and,  as  the  bed  of  fuel  burns  away  irregularly,  it  has  to  be 
levelled. 

When  the  coal  cakes  much  the  fire  has  to  be  broken  up  from  time  to  time  to  afford 
a  passage  to  the  air  through  the  grate.  The  several  furnaces  of  a  boiler  or  set  of  boilers 
should  be  fired  and  worked  in  rotation,  so  that,  if  possible,  no  two  furnace-doors  are 
open  at  the  same  time.  The  coaling  and  working  of  the  fires  must  be  done  as  rapidly  as 
possible  to  limit  the  inflow  of  cold  air  in  a  mass  through  the  open  doors  to  a  minimum. 

When  the  fires  are  kept  thin  while  the  draught  is  active,  or  when  the  fires  are  not 
kept  properly  levelled,  the  air  rushes  sometimes  with  great  violence  through  the  un- 
covered parts  of  the  grate,  producing  a  roaring  noise  and  severe  concussions  of  the 
boiler.  This  phenomenon  is  called  back-draught.  By  partly  opening  the  furnace- 
doors  or  closing  the  ashpit-doors  the  draught  is  generally  checked  sufficiently  to  stop 
the  violent  rush  of  air,  but  to  remedy  the  evil  the  fire  must  be  levelled  or  carried  a  little 
thicker. 

When  the  incandescent  fuel  throws  a  uniform  bright  light  below  the  grate  it  indi- 
cates that  the  fires  are  clean  and  burning  actively.  When  the  ashpits  are  dark,  either 
totally  or  in  parts,  it  indicates  an  accumulation  of  ashes  or  clinker  on  the  grates.  To 
clear  the  air-passages  the  hook-bar  is  run  through  the  interstices  of  the  grate  from  the 
ashpit,  and  when  much  difficulty  is  experienced  in  moving  the  hook-bar  back  and  forth 
between  the  grate-bars  it  indicates  the  formation  of  clinker.  Clinkers  adhering  to  the 
top  of  the  grate-bars  are  detached  by  means  of  the  slice-bar  introduced  through  the 
furnace-door,  and  are  then  removed  from  the  furnace.  Ashes  and  cinders  are  apt  to 
accumulate  in  the  corners  of  the  furnace ;  such  places  must  be  cleaned  out  and  the 


378  STEAM  BOILERS.  CHAP.  XVII. 

whole  grate  must  be  kept  covered  with  live  coal.  When  the  coal  is  friable  it  should  be 
disturbed  as  little  as  possible  with  the  slice-bar,  to  avoid  the  loss  of  small  coal  falling 
unburnt  through  the  grate. 

When  the  accumulation  of  ashes,  cinders,  and  clinker  on  the  grate  becomes  so  great 
that  they  cannot  be  removed  by  pricking  and  slicing,  the  fire  must  be  thoroughly 
cleaned  by  hauling  all  refuse  matter  from  the  furnace,  leaving  a  clean  bed  of  incandes- 
cent coal  on  the  grate.  This  cleaning  should  be  done  at  regular  intervals,  generally  not 
exceeding  twelve  hours,  but  depending  on  the  amount  and  kind  of  the  refuse  matter 
contained  in  the  coal.  That  the  cleaning  may  be  done  quickly  and  thoroughly  the  fire 
should  not  be  very  heavy,  but  it  should  have  a  sufficiently  thick  layer  of  incandescent 
coal  on  top  to  cover  the  grate  completely  after  the  refuse  has  been  removed.  The  fire- 
man pushes  back  the  top  layer  of  incandescent  coal  from  the  front  half  of  the  grate 
and  hauls  the  mass  of  refuse  below  it  from  the  furnace,  cleaning  the  grate  entirely. 
Then  he  hauls  all  the  clean  coal  from  the  back  of  the  furnace  to  the  front  of  the  grate ; 
he  works  the  mass  of  ashes  and  cinders  at  the  back  through  between  the  grate-bars, 
and  hauls  the  larger  of  pieces  of  slate  and  clinker  out  of  the  furnace  over  the  heap  of 
coal  in  front.  The  clean  coal  is  then  spread  evenly  over  the  grate  and  covered  at  once 
with  a  thin  layer  of  fresh  fuel. 

Some  firemen,  instead  of  cleaning  first  the  front  and  then  the  back  of  the  fire,  clean 
the  two  sides  of  the  furnace  in  succession,  using  the  slice-bar  to  move  the  top  layer  of 
clean  coal  from  the  side  to  be  cleaned  to  the  other  side. 

The  slack  of  anthracite  coal  can  be  burnt  only  when  mixed  with  a  certain  proportion 
of  lump-coal.  The  lumps  should  never  be  larger  than  a  cube  of  three  inches  a  side. 

The  dust  of  bituminous  coal  may  be  burnt  by  mixing  it  with  water  so  as  to  form  a 
cohering  mass  or  thick  paste.  The  evaporation  of  the  water  mixed  with  the  coal  ab- 
sorbs much  heat,  but  without  it  the  dust  would  fall  through  the  grate  or  be  carried 
into  the  flues  by  an  active  draught,  proving  thus  a  total  loss. 

The  friable,  free-burning  semi-bituminous  coals  are  frequently  mixed  in  equal  pro- 
portions with  caking  coals,  in  order  to  bind  the  small  particles  of  the  former  together 
and  prevent  their  falling  unconsumed  through  the  grate. 

Many  kinds  of  bituminous  coal  require  special  methods  of  firing,  in  order  that  their 
gaseous  products  may  be  completely  consumed  and  that  the  production  of  smoke  may 
be  prevented.  When  a  fresh  charge  of  coal  is  thrown  upon  the  fire  the  first  effect  pro- 
duced, as  it  becomes  heated,  is  the  evolution  of  a  mass  of  hydrocarbon  gases,  which 
make  latent  a  large  quantity  of  heat  and  require  a  larger  quantity  of  air  for  their  com- 
plete combustion  than  the  remaining  solid  portion  of  the  coal  or  coke.  On  this  account 


SBC.  3.  MANAGEMENT  OP  BOILERS.  379 

the  air-admission  through  the  door  into  the  furnace,  or  through  the  bridge-wall  into  the 
combustion-chamber,  may  be  regulated  by  registers,  which  are  opened  after  a  fresh 
charge  of  coal  has  been  thrown  upon  the  fire,  and  closed  when  the  evolution  of  hydro- 
carbon gases  ceases — that  is  to  say,  when  the  coal  burns  without  flame. 

When  the  furnaces  are  wide  side-firing  may  be  employed,  which  consists  in  throw- 
ing each  new  charge  of  coal  alternately  on  either  side  of  the  fire,  so  that  the  evolution 
of  hydrocarbon  gases  takes  place  only  on  one  half  of  the  grate,  while  on  the  other  half 
the  coked  coal  of  the  previous  charge  is  burnt. 

Some  kinds  of  free-burning  semi-bituminous  coal  are  burnt  to  best  advantage  by 
piling  each  fresh  charge  up  on  the  dead-plate  at  the  front  of  the  grate,  where  the  vola- 
tile ingredients  of  the  coal  are  expelled  by  the  heat  radiated  from  the  incandescent  fuel. 
As  these  gases  pass  through  the  furnace  and  mix  with  a  sufficient  quantity  of  air, 
which  passes  in  excess  through  the  grate,  they  ignite  and  are  completely  consumed. 
As  soon  as  the  mass  of  coal  on  the  dead- plate  becomes  converted  into  coke  it  is  pushed 
back  and  spread  over  the  grate. 

When  wood  is  to  be  used  as  fuel  in  a  furnace  designed  to  burn  coal  the  grate  has  to 
be  lowered  to  increase  the  capacity  of  the  furnace,  and  the  spaces  between  the  bars 
should  be  increased  in  width  by  omitting  a  number  of  grate-bars. 

3.  Management  of  Boilers  under  Steam. — That  the  boilers  may  furnish  a  uni- 
form supply  of  steam  the  fires  must  be  supplied  with  fuel  and  cleaned  in  regular  rota- 
tion, as  described  in  the  preceding  section,  and  the  water  in  the  boiler  should  be  kept, 
at  nearly  a  uniform  height.  When  the  opening  of  the  check  and  blow  valves  is  pro- 
perly adjusted  the  feeding  and  blowing  may  be  kept  up  continuously.  The  water- 
gauge  glass  is  generally  located  in  relation  to  the  tubes  and  back-connections  so  that  a 
proper  level  of  water  is  maintained  when  the  glass  is  kept  about  half-full  of  water. 
Previous  to  cleaning  a  fire  the  water  may  be  allowed  to  rise  a  few  inches  above  the  usual 
level,  so  that  during  the  process  of  cleaning  the  fires,  and  till  they  have  been  brought 
again  to  their  normal  state,  the  supply  of  feed- water  may  be  diminished. 

When  bituminous  coal  is  used  as  fuel  the  tubes  must  be  swept  at  regular  intervals, 
about  once  in  twenty-four  hours  or  less  frequently,  according  to  the  greater  or  less  ten- 
dency of  the  coal  to  form  deposits  of  soot. 

In  order  to  increase  the  evaporation  to  a  maximum  diminish  the  quantity  of  water 
blown  out  and  increase  the  temperature  of  the  feed- water  as  much  as  practicable ;  secure 
an  ample  air-supply  by  turning  the  fire-room  ventilators  and  windsails  to  the  wind ; 
keep  the  ashpits  wide  open  and  clear  of  ashes,  and  the  fires  clean  ;  use  coal  of  about 
egg-size  and  free  of  slack,  when  the  fuel  is  anthracite ;  and  regulate  the  thickness  of  the 


380  STEAM  BOILERS.  CHAP.  XVII. 

fires  according  to  the  force  of  the  draught  and  the  kind,  quality,  and  size  of  the  fuel. 
The  boilers  of  naval  vessels  are  generally  provided  with  a  steam-jet  in  the  chimney  for 
the  purpose  of  increasing  the  draught.  It  should  be  borne  in  mind  that  with  a  given 
boiler  the  rate  of  combustion  cannot  be  increased  advantageously  beyond  a  certain 
limit,  on  account  of  the  decrease  of  the  economic  evaporative  efficiency  of  the  boiler ; 
that  the  efficiency  of  the  boiler  may  be  greatly  diminished  by  foaming  with  an  increased 
evaporation ;  and  that  the  available  quantity  of  steam  furnished  by  a  boiler  may  be 
actually  diminished  when  the  rate  of  combustion  is  increased  by  forcing  the  draught. 
(See  section  6,  chapter  xii.) 

When  only  a  fraction  of  the  boiler-power  is  used  all  the  openings  of  the  uptake, 
furnace  and  ashpit  doors  of  such  furnaces  as  are  not  in  use  must  be  closed  tight  to  pre- 
vent the  inflow  of  cold  air.  Often  it  is  advantageous  to  keep  all  the  furnaces  in  use, 
but  to  diminish  the  effective  grate-surface  by  covering  the  back  of  the  grate  either  with 
a  thick  layer  of  ashes  or  by  a  wall  of  fire-brick  built  up  to  the  height  of  the  bridge-wall. 
The  latter  plan  should  be  adopted  only  in  case  the  reduced  boiler-power  is  to  be 
used  for  long  periods  during  which  no  necessity  will  arise  for  using  full  boiler- 
power. 

When  the  boilers  are  not  required  to  work  up  to  their  full  power  fuel  may  be  econo- 
mized by  burning  a  greater  proportion  of  slack  or  coal-dust,  and  by  sifting  the  ashes 
and  burning  a  portion  of  them  containing  particles  of  unconsumed  coal. 

Banking  a  fire  means  to  pull  the  coal  together  in  a  heap,  leaving  a  part  of  the  grate 
uncovered.  By  this  means  the  combustion  is  greatly  retarded,  and  the  cold  air  flowing 
in  through  the  uncovered  part  of  the  grate  checks  the  evaporation.  When  the  boilers 
are  not  to  be  used  for  a  certain  length  of  time,  but  fires  are  to  be  kept  in  them  to  keep 
the  water  hot,  the  fires  should  be  banked  and  covered  with  a  layer  of  ashes  or  slack,  and 
the  ashpit-doors  and  the  damper  should  be  nearly  closed. 

When  the  steam-supply  is  to  be  temporarily  diminished  while  the  boiler  is  in  opera- 
tion some  fires  may  be  banked,  and  the  draught  may  be  checked  by  closing  the  ashpit- 
doors  and  the  damper  and  by  opening  the  uptake  and  furnace  doors.  The  opening  of 
the  furnace-doors  should  be  avoided,  if  possible,  because  the  cold  air,  rushing  into  the 
furnaces  and  striking  the  highly-heated  plates,  causes  sudden  and  unequal  variations  of 
temperature,  which  produce  local  strains  resulting  frequently  in  permanent  injuries  to 
the  boiler. 

When  the  engines  are  stopped  suddenly,  but  the  boilers  have  to  be  kept  ready 
for  starting  again  shortly,  the  formation  of  steam  has  to  be  checked  as  quickly  as  pos- 
sible ;  to  this  end  open  the  furnace  and  uptake  doors,  close  the  ashpit-doors  and  dam- 


SKC.  3.  MANAGEMENT  OF  BOILERS.  381 

pers,  uncover  a  p"art  of  the  grate,  increase  the  feed- water  supply  and  the  quantity  of 
water  blown  out ;  utilize  the  steam  for  distilling  or  other  useful  purposes.  When  the 
steam-pressure  rises  to  the  limit  allowed  the  safety-valve  has  to  be  raised.  United 
States  naval  boilers  are  frequently  provided  with  a  bleeding-valve,  by  which  an  excess 
of  steam  may  be  discharged  from  the  boiler  into  the  condenser,  instead  of  being  allowed 
to  escape  through  the  safety-valve. 

The  safety-valve  should  always  be  opened  gradually.  When  it  is  suddenly  opened 
wide  the  steam,  rushing  from  it  with  great  violence,  is  apt  to  carry  a  mass  of  water  with 
it,  which  falls  in  a  shower  from  the  top  of  the  escape-pipe  on  the  deck.  When  the 
water-capacity  of  the  boiler  is  small  this  sudden  loss  of  water  may  even  cause  some 
parts  of  the  heating-surfaces  of  the  boiler  to  become  uncovered. 

In  the  indications  of  the  water-level  in  the  boiler  by  the  gauge-glass  proper  allow- 
ance must  be  made  for  the  oscillations  and  the  list  of  the  vessel,  and  the  gauge,  must  be 
tried  from  time  to  time  to  see  that  the  narrow  passages  are  not  choked  with  sediment  or 
scale.  When  the  water-passage  is  clear,  but  the  steam-passage  is  closed,  the  gauge- 
glass  will  remain  completely  filled  with  water.  When,  on  the  contrary,  the  steam-pas- 
sage is  clear  and  the  water-passage  is  choked  the  water  remains  at  a  constant  level  in 
the  glass  without  oscillating.  The  gauge-glass  must  be  blown  through  from  time  to 
time  by  opening  the  waste-cock  and  shutting  off  the  water  and  steam  cocks  alternately. 
If  this  does  not  clear  the  passages  it  is  necessary  to  run  a  wire  through  them. 

The  indications  of  the  water-gauges  are  frequently  very  uncertain  and  deceptive 
when  the  boiler  foams  ;  the  water  in  the  gauge-glasses  rises  and  falls  rapidly  and  in  an 
irregular  manner,  and  on  opening  the  gauge-cocks  a  mixture  of  steam  and  water  issues, 
producing  a  sputtering  sound. 

All  boilers  will  foam  to  some  extent  when  the  rate  of  combustion  exceeds  a  certain 
limit.  But  boilers  with  insufficient  or  low  steam-room,  contracted  water-surface,  and 
defective  circulation  are  especially  liable  to  foaming.  In  boilers  with  narrow  water- 
spaces  and  a  high  rate  of  combustion  the  water  is  frequently  lifted  in  a  mass,  so  that 
the  water-gauges  indicate  a  steady  level  of  solid  water  while  the  engines  are  in  opera- 
tion ;  but  as  soon  as  the  supply  of  steam  drawn  from  the  boiler  and  the  rate  of  evapora- 
tion are  diminished  the  water  falls  suddenly  to  its  true  level,  disappearing  sometimes 
entirely  from  the  gauges.  In  all  such  cases  it  is  necessary  to  check  the  evaporation  in 
order  to  stop  the  foaming ;  and  it  is  frequently  necessary  to  slow  down  the  engines  or 
open  the  furnace-doors  from  time  to  time  for  the  purpose  of  finding  the  true  level  of 
the  water  in  the  boiler. 

Vertical  fire-tube  boilers  and  horizontal  cylindrical  boilers  of  small  diameter  foam 


382  STEAM  BOILERS.  CHAP.  XVII. 

frequently  because  there  is  too  much  water  in  them,  in  consequence  of  which  their 
steam-room  and  the  area  of  the  water-level  are  simultaneously  reduced. 

Another  cause  of  foaming  is  the  presence  of  mud  or  dirt  of  a  mucilaginous  nature  in 
the  water,  which  may  be  recognized  by  the  appearance  of  the  water  in  the  gauge-glass. 
Also,  when  a  vessel  enters  a  river  in  coming  from  the  sea,  or  vice  versa,  the  boilers  are 
liable  to  foam  when  they  are  fed  directly  with  water  from  overboard.  In  all  such  cases 
it  is  advisable  to  change  the  water  in  the  boilers  as  rapidly  as  possible  by  opening  the 
surface  blow- valves  wide  and  feeding  strongly. 

In  reducing  the  saturation  of  boilers  the  surface  blow- valves  should  be  used  in  pre- 
ference to  the  bottom  blow- valves,  unless  the  vessel  rolls  so  much  that  the  former  would 
frequently  discharge  steam  instead  of  water. 

When  the  water  falls  below  its  usual  level  in  the  boiler  examine  the  feed  and  check 
valves  to  see  whether  they  are  open  and  in  operation.  The  latter  will  be  indicated  by 
the  clicking  noise  made  by  the  check-valve  as  it  rises  and  falls  in  its  seat ;  also  by  the 
temperature  of  the  pipe  immediately  below  the  valve,  which  should  be  comparatively 
cool  to  the  touch.  Close  the  blow-valves,  and  if  the  water  continues  to  fall  in  the 
boiler  it  must  be  owing  to  a  leak  in  the  boiler.  If  no  water  enters  through  the  check- 
valve,  although  the  feed-pump  is  throwing  water,  the  latter  may  escape  through  a  leak 
in  the  feed-pipe,  or  all  the  water  may  enter  some  of  the  other  boilers,  or  the  relief- valve 
of  the  pump  may  be  gagged  or  insufficiently  loaded.  If  the  pump  does  not  throw  any 
water  it  may  be  owing  to  air-leaks  in  the  stuffing-box  or  in  the  suction-pipe,  or  because 
the  valves  or  the  piston  are  leaking,  or  because  the  feed-water  is  too  hot.  The  feed- 
pump may  get  hot  because  the  check- valves  are  leaking.  When  the  valve  is  kept  open 
by  being  jammed  a  slight  jar  produced  by  tapping  the  valve-chamber  with  a  hammer  is 
sometimes  sufficient  to  seat  it.  When  some  matter  has  lodged  under  the  valve  and 
prevents  its  seating  it  may  be  washed  away  by  a  strong  feed  with  the  donkey-pump. 

In  case  the  water  should  suddenly  disappear  from  the  gauge-glass  on  stopping  the 
engines,  the  safety-valve  may  be  opened  wide  in  order  to  cause  the  boiler  to  foam  again 
and  the  water  to  be  lifted  sufficiently  to  cover  the  heating-surfaces  ;  at  the  same  time 
close  the  blow- valves  and  check  the  evaporation  by  opening  the  furnace  and  connection 
doors  and  by  covering  the  fires.  Do  not  put  on  the  feed  unless  you  are  sure  that  the 
water  has  not  fallen  low  enough  to  cause  the  plates  to  become  overheated. 

In  case  any  part  of  the  boiler  should  be  discovered  to  have  become  red-hot  in  conse- 
quence of  low  water,  or  the  furnace-crowns  to  be  collapsing,  do  not  open  the  safety- 
valve  or  change  the  working  of  the  engines,  and  especially  do  not  open  the  feed- 
valve,  but  haul  the  fires  from  the  furnaces  at  once  or  cover  them  with  wet  ashes,  and 


SEC.  3.  MANAGEMENT  OP  BOILEE&  383 

then  successively  close  the  stop- valve,  blow  the  water  from  the  boiler  through  the  bot- 
tom blow-valve,  and  open  the  safety-valve. 

Leaks  in  a  boiler  under  steam  become  manifest  by  a  hissing  sound  and  by  the  ap- 
pearance of  the  issuing  steam  or  water.  Serious  leaks  in  the  bottom  of  a  boiler  may  be- 
come known  only  by  the  falling  of  the  water-level  in  the  boiler,  and  by  an  increase  in 
the  quantity  and  in  the  temperature  of  the  water  in  the  bilge.  All  leaks  should  be 
closely  watched,  and,  in  case  they  are  found  to  increase  or  cause  serious  inconvenience, 
the  pressure  in  the  boiler  should  be  diminished,  if  the  leaks  cannot  be  stopped  other- 
wise. Small  leaks  of  water  frequently  stop  of  themselves  by  the  gradual  accumulation 
of  salt  deposited  by  the  issuing  water. 

Leaks  in  the  joints  of  manhole  and  handhole  plates,  and  leaks  caused  by  the  blow- 
ing-out of  a  bolt  or  rivet  in  the  boiler,  or  by  small  holes  in  the  feed  and  blow  pipes, 
may  be  temporarily  stopped  by  driving  into  the  holes  causing  the  leaks  slightly  taper- 
ing plugs  or  wedges  cut  from  dry,  soft  pine  wood. 

When  a  feed  or  blow  pipe  is  split  or  cracked  it  must  be  tightly  wrapped  with  stout 
cotton  canvas  painted  with  red  lead  on  the  side  nearest  the  pipe,  and  closely  bound 
with  marline.  Cut  the  canvas  in  long  strips  about  3  inches  wide,  and  let  each  turn 
overlap  the  preceding  one  half  its  width.  Wind  the  marline  around  it  in  such  a  direc- 
tion as  to  tighten  the  canvas  wrapping,  and  lay  each  turn  close  to  the  other,  pulling 
hard  to  prevent  its  stretching  or  shifting  afterwards. 

Leaks  in  the  boiler  may  sometimes  be  stopped  temporarily  by  covering  the  defective 
place  with  a  piece  of  plate-iron  fitting  closely  to  the  surface  and  held  firmly  in  position 
by  means  of  wedges  driven  against  the  bottom  or  side  of  the  vessel,  or  against  the  op- 
posite wall  of  the  boiler  or  of  an  adjoining  boiler.  To  make  the  joint  of  the  patch 
tight  use  either  canvas  painted  with  red  lead,  or  putty  made  of  white  and  red  lead  and 
stiffened  by  mixing  it  either  with  fine  iron  borings  or  with  hemp  chopped  very  fine. 

When  leaks  appear  in  the.  furnace-crowns,  the  water  issuing  either  from  cracks  in 
the  plates  or  from  the  seams,  it  is  best  to  haul  the  fires  from  the  respective  furnaces 
when  the  leaks  are  found  to  be  increasing  with  continued  use. 

The  leaks  of  tubes  may  be  caused  either  by  the  defective  joints  of  their  ends  or  by 
holes  or  rents  in  the  tubes.  In  the  latter  case  the  leak  may  be  stopped  by  plugging  the 
defective  tube  with  a  turned  soft  pine  plug  of  very  slight  taper.  These  plugs  are  about 
5  or  6  inches  long,  and  are  wrapped  with  canvas  painted  with  white  or  red  lead.  For 
the  front  end  of  the  tubes  the  diameter  of  the  larger  end  of  the  plug  is  slightly  greater 
than  the  internal  diameter  of  the  tubes,  and  the  small  end  is  swelled  out  by  the  water 
which  penetrates  the  pores  of  the  wood,  and  the  plug  is  thus  held  tightly  in  the  tube. 


384:  STEAM  BOILERS.  CHAP  XVIL 

When  the  leak  is  not  very  large  it  is  sufficient  to  plug  the  uptake  end  of  return-tube 
boilers,  so  that  the  water  does  not  run  out  through  the  uptake-doors  and  interfere  with 
the  working  of  the  fires,  but  runs  into  the  back-connections.  A  small  leak  may  some- 
times be  stopped  completely  by  securing  a  plug  within  the  tube  over  the  defective 
place.  When  the  leak  is  so  large  that  the  water  issuing  from  it  would  greatly  impair 
the  efficiency  of  the  fire  and  cause  a  large  accumulation  of  salt,  which  is  not  only  diffi- 
cult to  remove,  but,  by  closing  a  number  of  tubes,  may  seriously  impede  the  draught  of 
the  furnace,  both  ends  of  the  leaky  tube  have  to  be  plugged.  The  back-connection  end 
of  the  horizontal  fire-tubes  may  be  plugged  without  hauling  the  fires,  by  introducing 
from  the  front  end  of  the  boiler  a  plug  with  a  long  wedge  inserted  in  a  cross-cut  at  its 
outboard  end,  which  butts  against  the  back  wall  of  the  back-connection  when  the  plug 
is  in  place,  so  that  when  the  latter  is  driven  home  the  wedge  forces  it  tightly  against 
the  tube.  Sometimes  the  plug  itself  is  made  long  enough  to  reach  to  the  back  wall  of 
the  back-connection  when  it  is  home,  and  the  wedge  is  inserted  and  driven  in  the  end 
of  the  plug  projecting  within  the  tube.  The  part  of  the  plug  or  wedge  which  projects 
within  the  back-connection  soon  burns  away,  but  within  the  tube  the  plug  is  protected 
by  the  water  which  penetrates  its  pores.  After  the  plug  has  been  driven  in  the  back 
end  another  phig  is  driven  in  the  front  end,  as  described  above.  It  is,  however,  neces- 
sary to  lower  the  steam-pressure  greatly  before  commencing  this  operation. 

Sometimes  it  may  be  necessary  to  enter  the  back-connection  in  order  to  plug  a  tube 
effectually.  In  such  a  case  haul  the  fire  from  the  furnace  which  is  to  be  entered,  and 
bank  and  cover  up  with  ashes  the  fires  in  the  other  furnaces  of  the  boiler.  Open  the 
surface-blow  and  pump  water  into  the  boiler  from  the  sea,  so  as  to  reduce  the  tempera- 
ture of  the  water  in  the  boiler.  Then  open  the  safety-valve  and  give  to  the  vessel  a  list 
to  let  the  water  run  out  of  the  front  end  of  the  leaky  tube.  After  covering  the  grate, 
bridge- wall,  and  back-connection  of  the  empty  furnace  with  boards,  bags,  or  old  canvas, 
a  man  can  safely  enter  the  back-connection.  Then  the  tube  may  be  stopped  up  with  a 
wooden  plug  in  the  same  manner  as  described  above  for  the  front  end  of  the  tubes.  Or 
both  ends  of  the  tube  are  covered  with  cup-shaped  washers  filled  with  stiff  putty,  and,  to 
hold  them  in  place,  a  stout  iron  rod  is  put  through  the  tube,  so  that  its  ends,  on  which 
screw-threads  are  cut,  project  through  the  washers ;  the  latter  are  then  screwed  up 
tight  with  nuts. 

When  a  boiler  is  to  be  put  out  of  use  it  is  best  to  let  it  cool  off  gradually.  To  this 
end,  after  the  fires  are  hauled  from  the  furnaces,  all  the  doors  should  be  kept  closed  and 
the  steam  should  be  allowed  to  condense  gradually  in  the  boiler.  When  the  pressure 
has  fallen  nearly  to  that  of  the  atmosphere  the  safety-valve  is  to  be  raised  and  kept 


SBC.  4.  MANAGEMENT  OP  BOILEBS.  385 

open.  When  the  temperature  of  the  water  in  the  boiler  has  decreased  sufficiently  the 
water  may  be  pumped  out  of  the  boiler  when  the  latter  is  provided  with  a  valve  and 
pipe-connection  for  this  purpose,  or  the  water  may  be  allowed  to  run  out  into  the  bilge 
through  one  of  the  mudholes  in  the  bottom  of  the  boiler. 

When  the  boiler  has  to  be  cooled  off  quickly  for  the  purpose  of  cleaning  and  repair- 
ing it  in  an  emergency,  the  water  is  blown  out  through  the  bottom  blow- valve  as  soon  as 
the  fires  are  hauled.  Previously  the  steam  should  be  raised  to  the  highest  working 
pressure,  so  that  the  water  may  be  blown  out  as  completely  as  possible.  A  peculiar 
crackling  noise  in  the  blow-pipe,  produced  by  the  condensation  of  the  steam  as  it  comes 
in  contact  with  the  cold  water,  indicates  that  the  boiler  is  empty.  When  the  blow- 
valve  is  kept  open  after  the  steam-pressure  has  fallen  so  low  that  it  no  longer  balances 
a  column  of  water  equal  in  height  to  the  difference  between  the  levels  of  the  water  in 
the  boiler  and  of  the  sea- water,  the  latter  will  enter  the  boiler.  This  would  be  indicated 
by  the  sudden  cooling  of  the  blow-pipe.  The  height  to  which  the  water  in  the  boiler 
has  fallen  may  be  found  by  sounding  the  boiler  with  a  hammer.  As  soon  as  the  blow- 
valve  is  closed  the  safety-valve  is  raised,  and  all  the  furnace  and  connection  doors  are 
opened  and  the  manhole  and  mudhole  plates  are  taken  off  to  dry  and  cool  the  boiler. 
In  case  of  urgency  the  boiler  may  be  cooled  quickly  by  filling  it  with  cold  sea- water 
after  blowing  the  water  out,  afterwards  running  the  sea- water  out  into  the  bilge. 

Blowing  a  boiler  down  jars  it  severely,  especially  when  the  blow-valve  is  opened 
wide  ;  and  this  is  often  the  cause  of  leaks  in  the  boiler  and  m  the  pipes  connected  with 
it.  It  should  never  be  done  except  in  cases  of  great  emergency. 

4.  Foaming :  its  Causes,  Effects,  and  Prevention. — Foaming  or  priming 
means  that  the  water  in  the  boiler  is  in  a  state  of  violent  agitation,  rising  and  falling 
rapidly  in  the  form  of  waves,  or  that  the  steam  is  mixed  with  water  in  the  form  of 
spray.  Foaming  is  a  source  of  great  inconvenience,  and  not  unfrequently  of  danger,  on 
account  of  the  uncertain  and  wrong  indications  of  the  water-level  given  by  the  gauges  ; 
and,  as  the  water  is  carried  with  the  steam  into  the  cylinders,  it  causes  a  serious  loss  of 
efficiency  and  may  cause  a  breaking-down  of  the  engines. 

Foaming  is  made  evident  by  the  boiling-up  or  the  rapid  and  irregular  oscillations  of 
the  water  in  the  gauge-glass,  and  by  the  sputtering  sound  produced  as  the  mixture  of 
steam  and  water  issues  from  the  gauge-cocks.  When  the  water  is  carried  over  into  the 
cylinders  its  presence  is  made  known  by  a  clicking  noise  caused  by  the  partial  collapse 
of  the  piston-rings,  and,  when  the  water  is  present  in  large  quantities,  by  the  thumping 
of  the  piston  at  each  end  of  the  stroke. 

All  boilers  are  apt  to  foam  when  the  water  contains  much  mud  or  dirt  of  a  mucil- 


386  STEAM  BOILERS.  CHAP.  XVII. 

aginous  nature.  Soda,  introduced  into  the  boiler  to  neutralize  the  fatty  acids  contained 
in  the  feed-water,  often  produces  foaming.  The  various  organic  substances  introduced 
into  boilers  to  prevent  the  formation  of  scale  are  apt  to  produce  the  same  effect.  (See 
section  11,  cJiapter  xviii.)  The  engines  of  the  English  naval  vessel  Hecate  were  broken 
down  by  excessive  foaming  caused  by  the  lime  placed  in  her  boilers  to  preserve  them 
and  not  removed  before  getting  up  steam.  When  a  vessel  coming  from  the  sea  enters 
fresh  water,  or  from  a  river  enters  the  sea,  the  boilers  foam  frequently.  In  all  such 
cases  it  is  advisable  to  change  the  water  in  the  boiler  as  rapidly  as  possible  by  opening 
the  surface  blow-valves  wide  and  putting  on  a  strong  feed. 

The  plan  of  stopping  foaming  by  covering  the  surface  of  the  water  in  the  boiler  with 
a  layer  of  oil  or  molten  tallow  injected  through  the  feed-pumps  is  not  to  be  recommended. 
It  is  not  only  an  expensive  remedy,  but  the  decomposition  of  the  animal  or  vegetable  fats 
at  high  temperatures,  and  in  contact  with  metals,  produces  fatty  acids  which  are  very  de- 
structive to  boilers. 

Boilers  are  liable  to  foam  when  they  have  an  insufficient  and  low  steam-room,  a  con- 
tracted water-surface,  and  such  an  arrangement  of  the  internal  parts  as  to  render  the 
circulation  of  the  water  defective.  It  may  be  assumed  that  any  boiler  will  foam  more 
or  less  when  its  evaporation  exceeds  a-  certain  limit,  so  that  the  steam-bubbles  rise  so 
rapidly  as  to  carry  some  of  the  water  through  which  they  pass  along  with  them.  For 
this  reason  some  water-tube  boilers  are  provided  with  deflecting-plates  at  the  upper  ends 
of  the  tubes,  without  which  the  water  would  be  thrown  in  jets  from  the  tubes  into  the 
steam-space.  (See  figure  2,  Plate  XXVIII.,  and  section  10,  chapter  xi.) 

When  the  steam,  as  it  is  generated,  has  to  escape  in  large  masses  through  very  nar- 
row water-passages  separate  channels  must  be  provided  for  the  descending  water-cur- 
rents, else  the  meeting  of  the  two  currents  moving  in  opposite  directions  is  very  apt  to 
result  in  foaming,  or  sometimes  in  lifting  the  water.  The  latter  expression  means  that 
the  steam  does  not  rise,  as  it  is  generated,  through  the  overlying  mass  of  water,  but  ac- 
cumulates on  the  heating-surfaces,  so  that  water  appears  at  a  greater  height  in  the 
boiler  than  would  be  the  case  if  the  steam  and  water  occupied  their  natural  positions. 
Under  these  circumstances  the  heating-surfaces  which  are  kept  bare  of  water  are  liable 
to  become  overheated,  and  the  water-gauges  give  wrong  indications  of  the  quantity  of 
water  in  the  boiler.  Whenever  the  evaporation  is  checked  the  water  falls  to  its  true 
level.  Thus  it  frequently  happens,  in  small  boilers  worked  with  a  high  rate  of  combus- 
tion, that  the  water  disappears  suddenly  from  the  gauges  which  had  indicated  a  moment 
before  an  ample  supply  of  water  in  the  boilers.  The  overheating  of  the  metallic  sur- 
faces may  cause  the  water,  as  it  comes  in  contact  with  them,  to  assume  the  spheroidal 


SEC.  4.  MANAGEMENT  OP  BOILERS.  387 

state,  and  its  evaporation  to  take  place  in  an  intermittent,  explosive  manner,  thereby 
producing  rapid  oscillations  of  the  water-level  or  projections  of  water  into  the  steam- 
space. 

In  hanging  water-tubes  the  separation  of  the  ascending  and  descending  currents  is 
effected  by  an  inner  tube.  (See  section  10,  chapter  xi.) 

In  the  vertical  fire-tube  boiler  represented  in  figure  1,  Plate  XXVIII.,  the  internal 
annular  tank,  which  serves  as  a  steam-reservoir,  separates  also  the  ascending  and  de- 
scending currents;  the  steam  rises  from  the  crown  of  the  furnace  between  the  tubes,  and 
the  water  flows  downward  in  the  annular  space  between  the  tank  and  the  shell  of  the 
boiler. 

In  the  ordinary  marine  boiler  with  the  tubes  arranged  over  the  furnaces  the  great 
mass  of  steam  generated  on  the  furnace-crowns,  in  addition  to  the  steam  formed  on  the 
tube-surfaces,  has  to  rise  through  the  narrow  spaces  between  the  tubes  ;  while  in  the 
locomotive  type  of  boiler  the  steam  escapes  from  the  furnace-crowns  and  from  the  tube- 
surfaces  directly  to  the  steam-room.  This  difference  in  the  arrangement  of  the  heating- 
surfaces  is  the  principal  reason  why  the  rate  of  combustion  in  marine  boilers  cannot 
approach  remotely  the  rate  of  combustion  common  in  locomotive  boilers  without  pro- 
ducing violent  foaming.  To  lessen  this  evil  the  circulation  of  the  water  in  marine 
boilers  should  be  facilitated  by  leaving  wide,  unobstructed  passages  between  the  nests 
of  tubes  of  adjoining  furnaces.  Good  results  have  been  obtained  in  English  boilers  by 
separating  these  spaces,  by  means  of  removable  plates,  from  the  nests  of  tubes  so  that 
they  may  serve  exclusively  as  passages  for  the  descending  currents  of  water  flowing  to 
the  furnace-crowns.  In  the  boiler  designed  for  the  U.  S.  S.  Polos  similar  plates,  reach- 
ing from  the  upper  row  of  tubes  to  the  furnace-crowns,  were  attached  by  means  of 
socket-bolts  to  the  cylindrical  shell,  leaving  a  space  several  inches  wide  between  the 
shell  and  the  plate.  The  introduction  of  circulating-tubes  in  the  back-connections  has 
also  had  the  effect  of  lessening  foaming  in  some  cases. 

In  horizontal  cylindrical  boilers  the  water-surface  and  the  steam-room  both  diminish 
rapidly  as  the  height  of  the  water-level  is  increased,  and  this  circumstance  renders  this 
form  of  boiler  especially  liable  to  foaming.  This  effect  is  frequently  produced  when  the 
water  is  allowed  by  accident  to  rise  beyond  a  certain  height  in  the  boiler.  In  some  cases 
it  has  been  found  advantageous  to  cut  out  the  upper  row  of  tubes  and  plug  up  the  holes 
in  the  tube-sheets,  so  as  to  be  able  to  carry  the  water  lower  in  the  boiler,  the  loss  in 
evaporative  power  by  the  diminution  of  the  heating-surface  and  calorimeter  of  the  tubes 
being  far  less  than  the  gain  in  efficiency  due  to  lessened  foaming.  This  plan  was  adopted 
in  the  boiler  of  the  U.  S.  S.  Triana,  and,  to  make  it  possible  to  carry  the  water  below  the 


388  STEAM  BOILERS. 


CHAP.  XVII. 


top  of  the  back-connection,  a  false  top  was  built  in  the  connection,  and  the  space  thus 
formed  filled  with  plaster-of -Paris. 

Whenever  the  steam-pressure  is  suddenly  diminished  by  withdrawing  a  large  quan- 
tity of  steam  from  the  boiler,  the  temperature  of  the  water  will  be  so  much  higher  than 
the  boiling-point  corresponding  to  the  reduced  steam-pressure  that  a  sudden  evolution 
of  steam,  accompanied  by  violent  ebullition,  takes  place.  This  effect  is  produced  when 
the  steam-room  in  the  boiler  is  too  small,  or  when  the  engines  are  suddenly  started  at  a 
high  speed  or  are  racing,  or  when  the  safety-valve  is  all  at  once  thrown  wide  open.  In 
such  cases  the  steam  rushing  violently  to  the  opening  may  carry  along  with  it  a  large 
mass  of  water,  which  rises  as  a  wave  over  the  surface  of  the  water,  and,  when  the  steam- 
room  is  low,  may  be  carried  into  the  steam-pipe  and  flood  the  cylinders,  or  be  projected 
from  the  escape-pipe.  It  is  of  little  use  to  surround  the  opening  of  the  stop-valves  with 
deflecting-plates  which  are  to  throw  off  the  mass  of  water  carried  up  by  the  steam-cur- 
rent. The  evil  may  frequently  be  corrected  by  drawing  the  steam  equally  from  a  large 
area  by  the  use  of  perforated  dry-pipes ;  or,  if  these  cannot  be  applied,  a  second 
stop- valve  may  be  placed  on  the  boiler  which  takes  steam  at  some  distance  from  the 
original  stop-valve.  This  plan  is  far  more  effective  than  merely  enlarging  the 
original  stop-valve  in  order  to  diminish  the  velocity  of  the  steam  passing  through  its 
orifice. 

In  many  cases  it  will  be  found  necessary  to  increase  the  steam-room  by  the  addition 
of  a  steam-drum.  High  vertical  steam-drums  have  the  advantage  that  the  water  held 
suspended  in  the  steam  is  separated  to  a  great  extent  from  it  before  it  can  reach  the  top 
of  the  drum,  from  where  the  stop-valve  should  take  the  steam.  (See  also  section  1, 
chapter  xiii.) 

Superheaters  are  efficient  in  correcting  some  of  the  evils  of  foaming  by  increasing  the 
steam-room  and  by  evaporating  the  water  carried  along  with  the  steam.  (See  section  10, 
chapter  iii.)  It  is,  however,  found  that  foaming  causes  frequently  the  rapid  destruction 
of  superheaters.  (See  section  3,  chapter  xiii.) 

5.  Constituents  of  Saline  Matter  in  Sea-water. — The  proportion  of  saline 
matter  contained  in  the  waters  of  different  seas  varies  greatly.  According  to  Dr.  Mar- 
cet,  the  ocean  of  the  southern  hemisphere  contains  more  salt  than  that  of  the  northern 
hemisphere,  the  mean  specific  gravity  of  sea- water  near  the  equator  being  1.0277,  or 
intermediate  between  that  of  the  waters  of  the  northern  and  southern  oceans. 

Dr.  Ure  gives  the  following  proportions  of  saline  matter  in  1,000  parts  (by  weight)  of 
sea- water  from  different  localities :  "  The  largest  proportion  of  salt  held  in  solution  in 
the  open  sea  is  38,  and  the  smallest  32.  The  Red  Sea  contains  43  ;  the  Mediterranean, 


SEC.  5.  MANAGEMENT  OP  B01LEBS.  389 

38 ;  the  British  Channel,  35.5  ;  the  Arctic  Ocean,  28.5  ;  the  Black  Sea,  about  21 ;  and 
the  Baltic,  only  6.6." 

An  analysis  of  the  water  of  the  English  Channel  at  Brighton,  made  by  Dr.  Schweit- 
zer, gave  the  following  results — viz  :  its  specific  gravity  was  1.0274,  and  1,000  parts,  by 
weight,  contained — 

Water 964.74372 

Chloride  of  sodium 27.05948 

Chloride  of  magnesium 3.66658 

Chloride  of  potassium 0.76552 

Bromide  of  magnesium 0.02929 

Sulphate  of  magnesia 2.29578 

Sulphate  of  lime. . .-. 1.40662 

Carbonate  of  lime. .  0.03301 


Total  weight 1000.00000 

An  analysis  of  the  water  of  the  Mediterranean,  made  by  Dr.  Laurens,  gave  the  fol- 
lowing results — viz. :  its  specific  gravity  was  1.0293,  and  1,000  parts,  by  weight,  con- 
tained— 

Water 959.06 

Chloride  of  sodium 27.22 

Chloride  of  magnesium 6.14 

Sulphate  of  magnesia 7.02 

Sulphate  of  lime 0.15 

Carbonate  of  lime 0.09 

Carbonate  of  magnesia 0.11 

Carbonic  acid 0.20 

Potash..  0.01 


Total  weight 1000.00 

The  amount  of  carbonate  of  lime  contained  in  sea- water  is  insignificant.  According 
to  Bucholz,  100  parts  of  cold  water  are  capable  of  holding  in  solution  from  .00416  to 
.00625  parts  of  carbonate  of  lime.  The  French  chemist  Couste  states  that  water  loses 
entirely  its  power  of  holding  this  salt  in  solution  when  its  temperature  reaches  a  point 
lying  between  285°  and  300°  Fahr.  After  being  once  precipitated  the  carbonate  of  lime 
is  not  redissolved  when  the  temperature  of  the  water  is  lowered. 


390 


STEAM  BOILERS. 


CHAP.  XVIL 


When  water  contains  an  excess  of  carbonic  acid  the  carbonate  of  lime  is  converted 
into  an  acid  carbonate  of  lime,  which  is  much  more  soluble  in  water.  On  the  applica- 
tion of  heat  the  acid  carbonate  loses  a  portion  of  its  carbonic  acid,  and  the  neutral 
carbonate  of  lime  is  deposited  in  the  form  of  a  powder. 

The  solubility  of  sulphate  of  lime  is,  according  to  Regnault,  a  maximum  at  95° 
Fahr.,  when  100  parts  of  water  dissolve  0.254  parts  of  this  salt.  At  212°  Fahr.  100 
parts  of  water  dissolve  only  0.217  parts  of  this  salt ;  and,  according  to  Couste,  water 
loses  completely  its  power  of  holding  in  solution  the  sulphate  of  lime  when  its  tempe- 
rature reaches  a  point  lying  between  285°  and  300°  Fahr.  This  salt  is  more  soluble  in 
dilute  solutions  of  chloride  of  sodium,  and  it  is  insoluble  in  a  saturated  solution  of  the 
same  salt.  The  precipitated  sulphate  of  lime  is  redissolved  when  the  water  cools  down ; 
but  this  process  is  the  slower  the  higher  the  temperature  at  which  it  was  precipitated. 
When  the  deposit  is  formed  at  300°  Fahr.  it  takes  several  days  before  it  is  redissolved 
by  the  water,  even  if  the  quantity  is  small  relatively  to  the  water. 

The  chloride  of  calcium,  formed  by  a  reaction  between  the  carbonate  of  lime  and 
the  chloride  of  magnesium,  is  soluble  in  water,  and  undergoes  no  decomposition  in  the 
presence  of  water  at  the  temperatures  obtaining  in  steam  boilers. 

The  chloride  of  sodium,  or  common  salt,  which  forms  by  far  the  greatest  proportion 
of  the  saline  matter  of  sea- water,  undergoes  no  decomposition  by  heat.  Its  solubility  in 
water  is  nearly  the  same  at  all  temperatures  : 

100  parts  of  water  at  57°  Fahr.  dissolve  36  parts  of  this  salt. 
"      "  "  140°  Fahr.       "        37      "  " 

"      "  "  212°  Fahr.       "        40      "  " 

The  chloride  of  magnesium  is  very  soluble  in  water.  At  60°  Fahr.  100  parts  of 
water  dissolve  200  parts  of  this  salt.  It  is  decomposed  at  212°  Fahr.,  forming  hydro- 
chloric acid  and  magnesia ;  the  latter  substance  is  deposited  in  the  form  of  a  white 
powder,  while  the  former  enters  into  combinations  with  the  iron  of  the  boiler  and  with 
the  lime.  (See  sections  7  and  11,  chapter  xviii.) 

Sulphate  of  magnesia.— 100  parts  of  water  at  207°  Fahr.  dissolve  644  parts  of  the 
crystallized  salt ;  100  parts  of  water  at  58°  Fahr.  dissolve  104  parts. 
6.  Composition  of  Boiler-scale. 


Station. 

Fracture. 

Sulphate  of  lime. 

Carbonate  of  magn. 

Magnesia. 

Water. 

Hamburg  

Partly  crystallized 

8s  20 

?   ?C 

5nc 

6  e 

Mediterranean  . 

Amorphous  

8/1.  QA 

Z--J5 

2.  1A. 

•V3 
7.66 

°*5 

A  6c 

^•O^r 

I 

SKC.  7. 


MANAGEMENT  OF  BOILERS. 


391 


The  water  was  present  in  mechanical  combination.    (Engineering,  1866.) 
In  the  '  Third  Report  of  the  Admiralty  Committee  on  Boilers '  the  composition  of 
scale  from  the  boilers  of  various  ships  is  given — viz. : 


H.  M.  S. 

A  metkyst. 

H.  M.  S. 

Malabar. 

H  M.S. 
Fox. 

S.  S. 
Patrxlus. 

S.S. 
Vtlindra. 

Sulphate  of  lime  
Magnesia  

94.64 

2.88 

95-93 
•?.  10 

77-3° 
10.  SS 

96  37 
1.62 

91.38 
2.-?! 

Silica  

Traces. 

)                     j 

Traces. 

I          j 

I.4O 

Peroxide  of  iron  .... 

Traces. 

0.40      j 

5.80 

\    °-6°  \ 

1.  60 

Water  

2.41? 

6.00 

i-75 

T..T.Q 

In  the  boiler  of  the  S.  S.  Deccan  the  water  had  been  raised  to  ten  times  the  density 
of  sea-water,  so  that  the  brine  contained  in  100  parts- 
Chloride  of  sodium 27.76 

Chloride  of  magnesium 3.72 

Sulphate  of  magnesia 1.65 

Sulphate  of  potassa 0.87 

Water 66.00 

and  had  a  specific  gravity  of  1.224  at  60°  Fahr.    The  thick  saline  deposit  from  the  fur- 
nace-crowns of  this  boiler  contained  in  100  parts — 

Chloride  of  sodium 97.83 

Chloride  of  magnesium 0.59 

Sulphate  of  lime 0.56 

Peroxide  of  iron 0.02 

Water..  1.00 


100.00 

7.  Cousin's  Theory  of  the  Formation  of  Deposits  in  Steam  Boilers.— When 

sea- water  in  its  natural  state  is  evaporated  in  a  boiler  the  following  phenomena  are 
observed : 

I.  A  few  moments  after  ebullition  commences  the  water  in  the  boiler  grows  turbid, 
and  holds  in  suspension  first  free  magnesia,  then  carbonate  of  magnesia.  These  two  sub- 
stances are  present  in  small  quantities,  and  are  light,  flaky,  and  have  no  tendency  to 
agglomerate.  They  form  with  the  organic  and  earthy  substances  which  the  water  holds 


392  STEAM  BOILERS.  CHAP.  XVII. 

in  suspension  the  muddy  deposits  which  are  found  in  the  bottom  of  boilers  and  on 
horizontal  heating-surfaces. 

II.  By  the  continuance  of  ebullition  the  water  arrives  soon  at  the  point  of  saturation 
with  regard  to  the  sulphate  of  lime,  and  from  this  moment,  if  the  degree  of  saturation 
is  allowed  to  pass  the  point  where  the  motion  of  the  molecules  of  water  are  capable  of 
keeping  the  particles  of  sulphate  of  lime  mechanically  in  suspension,  these  particles  are 
deposited  as  a  crystalline  crust  on  all  surfaces  in  contact  with  water. 

III.  The  heating-surfaces  impart  to  the  water  in  contact  with  them  a  sufficiently 
high  temperature  to  make  it  supersaturated  as  far  as  the  sulphate  of  lime  which  it  con- 
tains is  concerned.      This  sulphate  is  then  deposited  on  the  plates  constituting  the 
heating-surfaces,  forming  there  at  once  a  thin  layer  of  incrustation,  whatever  may  be 
the  degree  of  concentration  of  the  mass  of  water.     Afterwards,  when  the  degree  of 
concentration  rises  above  the  point  mentioned  above  (see  II.),  the  particles  of  sulphate 
of  lime  spoken  of  in  the  same  paragraph  cling  to  this  layer  and  increase  the  thickness 
of  the  scale.     It  appears  that  -in  case  those  particles  which  are  precipitated  without 
being  in  contact  with  the  heating-surfaces  did  not  cling  to  such  a  layer  of  scale,  they 
would  not  adhere  to  the  metal  of  the  heating-surfaces,  and  would  form  merely  a  de- 
posit and  not  scale. 

IV.  When  the  fires  are  hauled  and  the  water  in  the  boiler  has  cooled  down,  that  por- 
tion of  the  muddy  deposit  which  the  water  held  in  suspension  by  the  motion  of  its  par- 
ticles produced  by  ebullition  falls  down  on  the  surfaces  of  the  boiler,  or  rather  on  the 
scale  which  covers  them.     This  extremely  thin  layer  of  mud,  lodged  in  the  depressions 
of  the  rough  surface  of  the  scale,  remains  there  mostly  when  vaporization  recommences. 
Then,  as  soon  as  the  water  reaches  again  the  above-mentioned  point  of  concentration, 
a  second  layer  of  sulphate  of  lime  is  formed  on  top  of  the  first  one,  but  separated 
from  it  by  a  film  of  magnesia  and  carbonate  of  magnesia  combined  with  a  little  oxide 
of  iron  and  organic  matter  which  give  a  yellowish  color  to  this  film.     Since  the  eva- 
poration is  very  active  on  the  crown-sheets  of  the  furnaces,  the  incrustation  forms  there 
very  rapidly ;  hence  the  scale  should  be  much  thicker  there  than  elsewhere.     But  the 
contrary  is  the  case,  because  as  soon  as  scale  is   formed  it  is  detached  by  the  con- 
tractions and  expansions  of  the  metal  occurring  every  time  the  intensity  of  the  fire 
varies.     Indeed,  it  is  found  that  the  scale  which  covers  this  portion  of  the  heating- 
surfaces  consists  generally  of  a  single  layer,  a  fracture  showing  no  intermediate  film. 
For  the  contrary  reason  the  scale  reaches  greater  thickness  at  points  of  less  intense 
heat,  where  it  is  composed  of  distinct  layers  separated  by  films,  each  layer  being  gen- 
erally less  thick  than  the  single  layer  on  the  furnace-crown. 


SBC.  9.  MANAGEMENT  OF  BOILERS.  393 

V.  The  fracture  of  the  incrustations  shows  an  amorphous  structure  throughout 
nearly  their  whole  thickness,  except  at  the  side  opposite  to  that  in  contact  with  the 
metal,  where  it  has  an  appearance  of  crystallization.  On  the  other  hand,  the  greater 
part  of  the  isolated  concretions  which  are  found  at  the  bottom  of  the  boiler  consist 
each  of  an  amorphgus  core  enveloped  by  crystalline  layers.  These  facts  indicate  that, 
at  the  moment  when  a  layer  is  deposited,  it  has  a  crystalline  character  due  to  the  pre- 
sence of  a  certain  proportion  of  water ;  but  after  having  been  in  contact  with  the  metal 
for  a  certain  length  of  time,  this  water  of  crystallization  is  set  free  and  the  scale  be- 
comes amorphous.  Contact  with  the  heating-surfaces  suffices  to  produce  this  effect, 
for  their  temperature  exceeds  always  570°  Fahr.,  and  it  is  known  that  390°  are  suffi- 
cient to  deprive  the  sulphate  of  lime  of  its  water  of  crystallization.  Besides,  it  is  easily 
conceived  that  this  calcination  is  less  complete  as  the  portions  of  scale  are  farther 
removed  from  the  metal,  and  is  nothing  at  the  face  in  contact  with  the  liquid.  (Ledieu.) 

8.  Prevention  of  the   Formation  of  Scale  in  Boilers. — Three  methods  are 
employed  to  prevent  the  accumulation  of  scale  in  marine  boilers — viz.  :  I.  Blowing-off 
a  portion  of  the  water  in  the  boiler  when  it  has  reached  a  degree  of  concentration  at 
which  deposits  would  be  formed,  and  replacing  it  by  ordinary  sea-water.      II.  Feeding 
the  boiler  with  water  from  a  surface-condenser  or  distilled  by  a  special  apparatus,  or 
with  sea-water  which  has  been  deprived  of  a  portion  of  its  salts  by  heating  it  to  a 
high  temperature  in  a  separate  vessel.     III.  Mixing  various  substances  with  the  water 
of  the  boilers,  which  prevent  the  formation  of  scale  either  by  mechanical  or  by  chemical 
action.     (See  section  11,  chapter  xviii.) 

9.  The  Hydrometer. — The  concentration  of  the  water  in  the  boiler  is  determined 
by  means  of  an  instrument  called  "hydrometer"  or  " salinometer,"  which  is  a  float 
having  a  constant  weight  and  measuring  by  the  depth  of  its  immersion  the  relative  bulk 
of  fluids  of  different  densities  having  the  same  weight. 

The  hydrometer  used  in  the  United  States  Navy  is  a  graduated  narrow,  cylindrical 
tube  closed  at  the  top.  The  lower  part  is  enlarged  to  give  buoyancy  to  the  instrument, 
and  terminates  in  a  small  globe  filled  with  shot,  which  serves  to  keep,  the  hydrometer 
floating  in  an  upright  position  (see  figure  147). 

These  instruments  are  generally  made  of  glass,  and  the  scale  is  marked  on  a  slip  of 
paper,  which  is  secured  within  the  narrow  tube.  Each  vessel  is  also  furnished  with  a 
standard  copper  hydrometer  of  similar  shape,  having  the  scale  engraved  on  the  narrow 
stem.  It  is  necessary  to  handle  these  latter  very  carefully,  since  any  indentation  would 
alter  the  relation  existing  between  the  bulk  and  the  weight  of  the  instrument,  and  con- 
sequently destroy  the  correctness  of  the  scale. 


394 


STEAM  BOILERS. 


CHAP.  XVII. 


Fig.  147. 


32 


In  order  to  graduate  this  instrument  it  is  first  placed  into  a  vessel  containing  dis- 
tilled water  of  a  fixed  temperature,  and  the  point  to  which  it  is  immersed  is  marked 
zero.  Then  sea-salt  is  dissolved  in  the  water  in  the  successive  proportions  of  one,  two, 
three  pounds,  etc.,  of  salt  to  thirty- two  pounds  of  water,  and  the  respective  points  to 

n  which  the  instrument,  floating  in  the  solu- 

tion, is  immersed  at  a  uniform  temperature 
are  marked  ^,  fa,  ^,  etc.  Each  of  these 
divisions  is  further  subdivided  into  halves 
and  quarters.  The  temperature  for  which 
the  hydrometer  is  graduated  must  be  mark- 
ed on  the  scale.  Hydrometers  have  some- 
times three  different  scales,  corresponding 
respectively  to  temperatures  of  190°,  200°, 
and  210°  Pahr. 

Approximately,  for  an  increase  of  10°  in 
temperature  the  density  of  the  solution, 
as  indicated  by  the  hydrometer,  decreases 
by  one-eighth  of  a  division — in  other  words, 
the  hydrometer  will  indicate  a  concentra- 
tion which  is  one-eighth  of  a  thirty-sec- 
ond less  than  the  true  one  when  the  tem- 
perature of  the  solution  is  10°  higher 
than  the  temperature  for  which  the  scale 
was  constructed.  It  is,  therefore,  necessary 
to  keep  a  thermometer  immersed  in  the 
water  which  is  drawn  from  the  boiler  into 
a  suitable  vessel  for  the  purpose  of  testing 
its  concentration.  (See  section  10,  chap- 
ter xv.) 

The  divisions  of  the  scale  constructed 
in  the  aforesaid  manner  are  not  uniform, 
but  decrease  in  length  as  the  degree  of  con- 
centration increases.  The  following  inves- 
tigation will  show  the  relation  which  would  exist  between  the  lengths  of  successive 
divisions  of  the  scale  in  case  the  density  of  the  solution  was  proportionate  to  the  sum 
of  the  densities  of  its  separate  constituents : 


SCALE  DEVELOPED 
FULL  SIZE 

<f& 

190 
0 

<&r<* 
200 

0 

210° 
0 

1 

1 

1 

82 

Ht 

V 

32 

:? 

32 

I1 

••3' 

82 

HJ 

3 

33 
3 

32 

-1 
8 

32 

33 

33 

Sue.  10. 


MANAGEMENT  OP  BOILERS.  395 


If  w  =  the  weight  of  water  contained  in  the  solution, 
v  =  its  corresponding  volume, 

10 
d  =  the  volume  of  salt,  the  weight  of  which  is  go  j 

and  if  x,  #„  #,„  #1U,  etc.,  represent  the  volumes  of  the  solution  displaced  by  the  hy- 
drometer at  successive  degrees  of  concentration  corresponding  to  0,  -£?,  -fa,  -fo,  etc.,  of 
the  scale,  then,  since  the  weight  of  these  volumes  is  equal,  we  have  the  equations  : 
w  33  w  34  w  35w  , 

'   :=  320  +  2  d)    "  -  "" 


consequently 

32  (v  +  d)     .        _  32  (v  +  2  d)  32fr  +  3d)         .    . 

**  =     ~~33V~        '     "  ~        ~34¥~  '"   •          ~35¥~ 

and  the  length  of  each  division  is  proportionate  to 


x       x  -x  x 

l~ 


33  v  33 

.  32  Q  +  d)        32(t>+2d)  _  32  .  tt-32^ 

*'         "  33 »  34«  -  33       ~34~~ 

oo  /^.    i    q  rf\  qo      «.          qo  /7 

O^  ^C  — j—  O  U/j  &£        V   —   O^  C*' 


The  density  of  the  brine,  however,  does  not  increase  proportionately  with  the  weight 
of  salt  held  in  solution,  but  a  condensation  takes  place  when  salt  is  dissolved  in  water, 
which  appears  to  be  greatest  for  very  much  diluted  brines  ;  when  100  ounces  of  water 
are  mixed  with  34  ounces  of  common  salt  the  decrease  in  volume  is  equal  to  4  per  cent, 
of  the  sum  of  their  respective  volumes. 

The  presence  of  saline  matter  in  water  has  the  effect  of  raising  its  boiling  point,  and 
this  property  has  been  made  use  of  to  determine  the  concentration  of  the  solution. 
For  water  containing  the  usual  proportions  of  the  salts  of  sea- water  the  boiling  tem- 
perature under  mean  atmospheric  pressure  is  raised  very  nearly  one  degree  for  each  ad- 
ditional 2.58  per  cent,  of  saline  matter. 

The  specific  heat  of  sea- water  is  .82,  that  of  fresh  water  being  1.00. 

1O.  Influence  of  Temperature  and  Pressure  on  the  Limit  of  the  Satura- 
tion of  Water  in  a  Boiler. — The  hydrometer  indicates  the  density  of  the  water  in 
the  boiler  due  to  the  saline  matter  held  in  solution,  but  gives  no  indication  of  the  rela- 
tive quantities  of  the  different  salts  constituting  this  saline  matter.  The  formation  of 
scale  depends  chiefly  on  the  quantity  of  sulphate  of  lime  present  in  the  water,  and  this 
salt  will  be  deposited  when  the  temperature  reaches  a  certain  point,  whatever  the  con- 


396 


STEAM  BOILERS. 


CHAP.  XVII. 


centration  of  the  water,  as  indicated  by  the  hydrometer,  may  be.  By  reference  to 
Table  XXXVIII.  it  will  be  seen  that  when  the  temperature  of  the  water  becomes  264° 
it  can  no  longer  hold  the  whole  quantity  of  sulphate  of  lime  present  in  ordinary  sea- 
water,  and  when  the  temperature  rises  to  280°  it  cannot  hold  any  of  this  salt  in  solu- 
tion. Under  these  circumstances  the  amount  of  deposit  formed  is  in  the  direct  ratio  of 
the  quantity  of  this  salt  introduced  into  the  boiler  with  the  feed- water ;  and  since 
blowing-off  necessitates  an  increase  in  the  quantity  of  feed- water,  it  increases  instead  of 
diminishing  the  formation  of  a  deposit  of  sulphate  of  lime  and  magnesia,  besides  wast- 
ing the  heat  imparted  to  the  water  which  is  blown  off,  and  introducing  additional  quan- 
tities of  air  and  of  the  destructive  chloride  of  magnesium  into  the  boiler.  The  only 
advantageous  effect  of  blowing-off  under  these  conditions  is  the  removal  of  the  particles 
of  lime  and  magnesia  kept  in  suspension  mechanically  by  the  currents  of  water  in  the 
boiler. 

Supposing  that  by  feeding  from  the  sea  the  concentration  of  the  water  in  the  boiler 
is  raised  to  -fa  on  the  scale  of  the  hydrometer,  and  when  this  point  is  reached  the  sea- 
feed  is  shut  off  and  the  supply  of  distilled  water  from  the  surface-condenser  is  substi- 
tuted, no  more  lime-salts  will  be  introduced  and  no  more  scale  will  be  deposited,  but  the 
hydrometer  will  still  indicate  •&. 

TABLE    XXXVIII. 


Absolute  pres- 
sures in 
atmospheres. 

Temperatures  of 
sleam,  correspond- 
ing to  pressures, 
in  degrees  Fahr. 

Density  of  water 
at  a  temperature 
of  59°  Fahr. 

Weight  of  sulphate 
of  lime  contained  in 
100  parts  of  the 
water  in  the  boiler. 

Total  weight  of  sa- 
line matter  con- 
tained in  100  parts  of 
the  water  in  boiler. 

Degrees  of  concen- 
tration indicated 
by  hydrometer. 

Temperatures  at 
which  the  water 
would  boil  under 
mean  atmospheric 
pressure. 

I.OO 

212 

1.0990 

O.6OOO 

13979 

si 

216.32 

1-25 

224 

1.0768 

0.4683 

IO.9I2 

3f 

215.42 

i-5° 

234 

1.0589 

°-3834 

8-935 

3| 

214.52 

i-75 

243 

I.04S9 

0-3055 

7.120 

2i 

214.16 

2.0O 

251 

1.0344 

0-2335 

5-442 

«f 

213.62 

2.25 

258 

1.0245 

0.1688 

3-934 

if 

213-39 

2.50 

264 

I.Ol62 

0.1132 

2.639 

1 

213-35 

2-75 

270 

1.0078 

0.0551 

1.285 

| 

213-34 

3.00 

275 

I.OOO2 

O.OOI2 

0.030 

i 

213-33 

3-25 

3-5° 

280 
285 

|-  the  water  cannot  hold  any  portion  of  sulphate  of  lime  in  solution. 

The  foregoing  table  contains  the  conditions  accompanying  the  saturation  of  sea- 
water  with  regard  to  the  sulphate  of  lime  at  various  pressures  and  temperatures.  The 
data,  adapted  to  our  hydrometric  scale  and  to  Fahrenheit's  thermometric  scale,  are 
selected  from  a  table  prepared  by  Couste.  It  is  based  on  the  assumption  that  sea- water 


SBC.  11.  MANAGEMENT  OP  BOILERS.  397 

in  its  natural  state,  and  hav-ing  a  density  of  1.026,  contains  0.15  per  cent,  of  sulphate  of 
lime,  2.65  per  cent,  of  chloride  of  sodium,  and  0.70  per  cent,  of  other  substances,  or  in 
all  3.50  per  cent,  of  saline  matter  and  96.50  per  cent,  of  fresh  water. 

11.  Calculation  of  the  Quantities  of  Water  and  Heat  lost  by  Bio  wing-off. 

— In  order  to  maintain  the  water  in  the  boiler  at  a  certain  concentration  the  quantity  of 
water  extracted  by  blowing  must  bear  to  the  quantity  of  water  fed  into  the  boiler  the 
same  ratio  as  the  number  indicating  the  concentration  of  the  feed- water  to  the  number 
indicating  the  concentration  of  the  water  in  the  boiler. 
Let  x  represent  the  number  on  the  hydrometer  indicating  the  density  of  the  feed- water ; 

"  y         "        the  number  on  the  hydrometer  indicating  the  density  of  the  water  in 
the  boiler ; 

"    s         "        the  number  of  pounds  of  water  evaporated  in  a  unit  of  time  ; 

"   b         "        the  number  of  pounds  of  water  in  the  brine  which  is  blown  off. 

Supposing  the  quantity  of  water  in  the  boiler  to  remain  the  same,  then  the  quantity 
of  salt  blown  off  in  a  unit  of  time  must  be  equal  to  the  quantity  of  salt  introduced  with 
the  feed-water  in  a  unit  of  time,  in  order  to  maintain  the  concentration  at  a  fixed  point. 
This  relation  may  be  expressed  by  the  following  equation : 

x  (s  -f-  b)  =  y  5  /  hence  (s  -j-  b) :  b  : :  y  :  x, 
which  proves  the  above  rule. 

In  calculating  the  loss  of  heat  by  blowing-off  absolute  accuracy  cannot  be  attained, 
because  the  specific  heat  of  sea- water  at  different  densities  has  not  been  ascertained.  It 
has  been  taken  as  being  the  same  for  all  densities  as  ordinary  sea- water — viz.,  0.82 
—although  for  greater  densities  it  is  probably  smaller.  Further,  since  the  boiling-point 
of  sea- water  at  different  concentrations  has  not  been  ascertained  for  pressures  higher 
than  the  atmospheric  pressure,  no  account  has  been  taken  in  the  following  example  of 
any  increase  of  temperature  due  to  the  higher  degree  of  concentration.  For  simplicity's 
sake  the  temperature  of  the  water  may  be  taken  as  representing  the  units  of  heat  con- 
tained in  each  unit  of  weight.  The  error  due  to  these  causes  is  slight  and  practically 
unimportant.  The  method  of  calculating  the  loss  of  heat  by  blowing-off  will  be  ex- 
plained by  the  following  example : 

Supposing  the  temperature  of  the  feed-water  to  be  110°,  its  concentration  7V  on  the 
scale  of  the  hydrometer,  the  steam-pressure  in  the  boiler  35  Ibs.  per  square  inch  above 
the  atmosphere,  what  percentage  of  the  total  heat  imparted  to  the  water  in  the  boiler  is 

lost  by  blowing-off  when  the  density  of  the  water  is  kept  at  -     -  on  the  scale  of   the 

oH 

hydrometer  1 


398  STEAM  BOILERS.  CHAP.  XVII. 

Regarding  the  weight  of  water  evaporated  as  unity,  the  weight  of  fresh  water 
contained  in  the  brine  blown  off,  represented  by  b,  bears  to  the  weight  of  fresh 
water  contained  in  the  feed  the  following  proportion — viz.:  6  :  (1  +  6)  ::  1  :  1.76  ;  hence 

b  =  A  =  1.333. 

1  Wi  V  1  7^ 

The  total  weight  of  brine  blown  off  is  consequently  =  1.333  -f  -  -  =  1.406 ; 

o& 
and  the  total  weight  of  feed- water  for  each  pound  of  water  evaporated  =  2.406. 

The  temperature  of  steam  at  a  pressure  of  35  Ibs.  above  the  atmosphere  is  280°  in 
round  numbers.  The  units  of  heat  present  in  the  feed  required  for  each  pound  of 
water  evaporated  are  (2.406  X  110  x  .82)  =  217.02. 

The  units  of  heat  required  to  raise  the  amount  of  water  blown  off  from  110°  to  280° 
are  equal  to  1.406  x  (280  -  110)  .82  =  196.00. 

Total  units  of  heat  present  in  each  pound  of  steam  =  1199.4 

"        "          "  "       in  water  blown  off  =  (1.406  x  280  x  .82)=    322.8 


Total  units  of  heat  in  water  and  steam  =  1522.2 

"        "  "      present  in  feed-water  =    217.0 


Total  units  of  heat  communicated  to  the  water  =  1305.2 

Percentage  of  heat  in  water  blown  off  in  terms  of  total  heat  expended  =  -    ^K  ^    =  14.94 


per  cent. 

12.  Cleaning  and  Scaling  Boilers.  —  The  boilers  should  be  cleaned  of  soot  and 
ashes  as  soon  as  possible  after  the  fires  are  hauled.  The  tubes  are  to  be  swept  first, 
commencing  with  the  top  row  of  each  tube-box.  Before  commencing  to  sweep  the  tubes 
turn  the  ventilators  away  from  the  wind  and  close  the  furnace  and  ashpit  doors,  so  that 
as  little  dust  as  possible  may  fly  about  the  fire-room  ;  but  open  all  the  connection-doors 
to  let  the  draught  carry  the  soot  or  ashes  up  the  chimney. 

Tube-brushes  are  made  either  of  wire  or  of  coir.  They  should  fit  the  tubes  snugly 
so  that  it  requires  some  force  to  push  them  through,  because  they  should  not  merely 
remove  the  loose  soot,  but  detach  also  the  hard  carbonaceous  scale  which  covers  the  fire- 
surfaces  of  the  tubes.  This  scale  frequently  clings  so  tenaciously  to  the  surfaces  that  it 
has  to  be  scraped  off. 

Tube-  scrapers  consist  of  steel  strips  secured  to  circular  end-pieces  and  bent  so  as  to 
form  ridges  running  at  an  angle  with  the  axis  of  the  tool.  An  efficient  scraper  is  formed 


SBC.  12.  MANAGEMENT  OF  BOILERa  399 

by  long,  thin  steel  strips  bent  to  a  spiral  shape,  which  are  secured  to  short,  cylindrical 
end-pieces,  and  can  be  adjusted  to  a  greater  or  less  diameter  by  moving  a  nut  in  the 
direction  of  the  axis  of  the  tool. 

Deposits  of  salt  from  leaks  which  may  have  accumulated  in  or  around  the  tubes 
must  be  carefully  removed  with  a  scraper  or  long  chisel.  In  the  narrow  spaces  between 
vertical  water-tubes  such  deposits  are  frequently  very  difficult  to  remove,  unless  they 
are  loosened  by  soaking  them  for  a  long  time  in  fresh  water.  For  this  purpose  a  dam 
is  built  up  at  both  ends  of  the  tube-box,  and  water  is  kept  in  the  latter  at  such  a  height 
as  to  cover  the  deposits  of  salt.  Such  deposits  may  also  be  loosened  by  directing 
against  them,  by  means  of  a  hose,  a  strong  stream  of  water  thrown  by  a  force-pump. 
But  in  no  case  should  water  be  used  in  the  flues  or  connections  unless  the  tubes,  con- 
nections, and  furnaces  have  been  thoroughly  cleaned  of  soot  and  ashes. 

After  the  tubes  have  been  cleaned  remove  the  soot  from  the  uptake  and  back-con- 
nections ;  scrape  the  plates  clean  of  scale  and  salt,  and  sweep  them  off  with  a  stiff 
broom.  The  furnaces  and  ashpits  are  to  be  cleaned  in  the  same  manner  after  the  grate- 
bars  have  been  removed.  The  grate-bars  are  to  be  cleaned  by  knocking  clinkers  and 
cinders  off  with  a  scaling-hammer.  Cast-iron  bars  which  are  much  broken,  burnt,  or 
bent  have  to  be  replaced  with  new  ones ;  wrought-iron  bars  have  to  be  repaired  or 
straightened. 

The  chimney  is  to  be  swept  and  scaled  periodically  on  the  inside.  When  bitumi- 
nous coal  is  burnt  the  accumulation  of  soot  in  the  chimney  becomes  so  great  that  it 
frequently  catches  fire  and  causes  serious  injury  to  the  chimney  unless  it  is  swept  off 
periodically. 

The  outside  of  boilers  must  be  cleaned  of  salt  deposited  from  leaks  after  every  run. 
When  the  leak  cannot  be  repaired  before  the  boilers  are  put  in  use  again  the  deposits 
which  close  a  leak  should  not  be  disturbed.  Special  attention  must  be  paid  to  the 
cleaning  of  the  front  of  boilers,  where  salt  accumulates  in  consequence  of  the  water 
leaking  from  the  water-gauges.  The  lower  part  of  the  boiler-front  is  generally  covered 
by  a  coating  of  ashes,  which  cling  to  the  boiler  when  they  are  wetted  after  hauling  them 
from  the  furnaces  and  ashpans.  The  bottom  of  boilers  is  frequently  found  covered  with 
salt  and  dirt  deposited  by  the  bilge- water  which  is  washed  up  against  the  boiler  by  the 
rolling  of  the  vessel.  Dry  ashes  and  dust  accumulate  on  the  top  of  boilers,  and  must 
be  swept  off  from  time  to  time. 

The  water-gauges,  salinometer-pots  and  their  pipes,  and  other  attachments  must  be 
cleaned  not  only  on  the  outside,  but  must  be  disconnected  so  as  to  clear  their  passages 
of  scale  and  sediment.  Valves  and  cocks  must  be  reground  and  packed,  if  necessary. 


400  STEAM  BOILERS.  CHAP.  XV1L 

Valve-stems  and  plug-cocks  must  be  greased  with  oil  or  tallow,  and  the  articulations  of 
safety-valve  levers  must  be  cleaned  and  oiled. 

The  outside  of  boilers  must  always  be  kept  covered  with  a  heavy  coat  of  paint, 
which  will  require  frequent  renewal  at  the  front  and  bottom,  where  the  leakage  of  water 
from  the  gauges  and  the  manholes  and  mudholes,  the  wetting  of  ashes,  and  the  wash- 
ing-up of  the  bilge-water  render  the  boiler  especially  liable  to  corrosion,  while  the 
frequent  cleaning  and  scraping  soon  wears  off  the  coat  of  paint.  For  painting  the 
shell  of  boilers  either  red  lead  or  a  brown  metallic  paint  prepared  from  the  brown 
oxide  of  iron  is  used.  The  furnaces,  connections,  uptakes,  and  the  inside  of  chimneys 
should  receive  a  coat  of  the  same  paint  when  the  boilers  are  to  be  put  out  of  use  for 
some  time.  The  inside  of  steam-drums,  if  accessible,  should  be  kept  covered  with  a 
heavy  coat  of  lead  or  brown  metallic  paint,  especially  the  lower  part  of  horizontal 
drums,  where  water  is  apt  to  collect.  The  cast-iron  of  connection,  furnace,  and  ash- 
pit doors  may  be  painted  with  lamp-black  and  oil,  or  may  be  simply  oiled.  Some  engi- 
neers paint  the  connection-doors  white,  in  order  to  make  the  fire-room  brighter.  In 
no  case  should  the  iron  of  boilers  be  whitewashed,  unless  it  has  first  received  a  heavy 
coat  of  paint,  because  the  lime  absorbs  moisture,  and  thus  would  promote  corrosion. 
The  outside  of  chimneys,  the  hatch-gratings,  ventilators,  etc.,  may  be  painted  with 
asphaltum.  In  no  case  should  paint  be  applied  to  any  part  of  the  boiler  before  it  is 
thoroughly  dried,  cleaned,  and  scaled,  so  that  the  paint  may  cover  the  clean  body  of 
the  metal. 

The  scaling  of  boilers  should  be  commenced  as  soon  as  they  have  cooled  off  suffi- 
ciently to  be  entered,  for  when  the  scale  is  still  damp  it  can  frequently  be  removed  much 
more  easily  than  after  it  has  got  quite  dry.  As  long  as  the  thickness  of  the  scale  does 
not  exceed  the  thickness  of  ordinary  writing-paper  it  should  not  be  disturbed,  as  it 
forms  the  best  protection  of  the  iron  against  corrosion ;  but  as  it  grows  thicker  its 
low  thermal  conductivity  produces  a  perceptible  diminution  of  the  evaporative  effi- 
ciency of  the  boiler,  and  exposes  the  plates  to  the  danger  of  being  burnt.  The  expan- 
sion and  contraction  of  the  plates  cause  thick  scale  to  crack  and  to  become  partially 
detached  from  the  plates,  and  in  this  condition  the  scale  favors  the  corrosion  of  boilers 
by  admitting  and  retaining  moisture  in  contact  with  the  plates. 

It  has  been  recommended  to  loosen  the  scale,  before  commencing  the  operation  of 
cleaning  the  boiler,  by  the  sudden  expansion  or  contraction  of  the  plates  or  tubes.  This 
might  be  done  by  admitting  cold  water  into  the  boiler  immediately  after  hauling  the 
fires  and  blowing  the  hot  water  out  of  the  boiler  ;  or  by  admitting  a  large  mass  of  steam 
into  the  cooled-off  boiler  and  allowing  it  to  condense  there  ;  or  by  making  a  light  fire  of 


SEC.  12.  MANAGEMENT  OP  BOILERS.  401 

wood-shavings  in  the  furnaces  or  connections.  The  latter  plan  has  resulted  in  several 
instances  in  burning  the  boiler.  But  all  these  methods  should  be  avoided,  as  the  sudden 
expansion  and  contraction  of  the  plates  is  always  injurious  to  the  boiler. 

The  scale  on  the  plates  must  be  chipped  off  with  scaling-hammers  or  wedged  off  with 
scaling-bars.  These  tools  must  not  be  ground  to  a  sharp  edge,  and  the  chipping  must 
be  done  carefully  to  avoid  making  indentations  in  the  surface  of  the  iron  and  injuring 
the  rivet-heads ;  where  such  indentations  are  made  the  scale  which  is  subsequently 
formed  adheres  more  tenaciously,  and  the  iron  is  more  readily  attacked  by  corrosion. 
Special  care  must  be  taken  in  scaling  the  tube-sheets  to  avoid  injuring  the  tube- 
ends.  The  crown-sheets  of  furnaces  are  generally  scaled  first.  The  scale  should  be  re- 
moved completely  from  the  plates  wherever  they  are  accessible,  especially  between  the 
rivet-heads  and  at  the  edges  of  laps,  and  around  the  crow-feet  or  the  heels  of  braces. 
The  narrow  water-spaces  around  the  back-connections  are  frequently  not  accessible  for 
thorough  scaling  unless  handholes  are  cut  at  suitable  places  in  the  shell. 

The  fire-tubes  of  marine  boilers  are  generally  spaced  so  closely  that  the  greater  por- 
tion of  their  surfaces  is  not  accessible  for  scaling.  The  vertical  spaces  between  these 
tubes  must  be  kept  clear  by  running  a  scaling-bar  through  them,  by  which  means  the 
scale  may  be  detached  from  the  tubes  in  flakes.  Various  devices  for  making  the  tubes 
readily  removable  for  scaling  have  been  tried,  but  have  not  given  satisfactory  results. 
When  the  accumulation  of  scale  on  the  tubes  becomes  very  great  it  will  be  necessary  to 
remove  a  sufficient  number  of  tubes  from  the  boiler  to  make  the  remaining  ones  accessi- 
ble for  scaling. 

Water-tubes  can  be  scaled  by  running  through  them  a  steel  bar  with  a  cutting  edge 
at  the  end,  or  by  boring  out  the  scale  with  Garviri's  scaling-tool,  consisting  of  a  revolv- 
ing cutter  worked  by  a  wrench,  and  fed  by  turning  a  screw  which  passes  through  the 
tube  and  is  secured  and  centred  at  both  ends.  Care  is  required  in  working  and  adjust- 
ing these  tools  so  as  not  to  cut  into  the  metal  of  the  tube. 

The  shell  of  the  boiler  in  the  water  and  steam  spaces  must  be  scraped  clean  of  mud 
and  rust,  all  the  loose  scale  must  be  knocked  off  the  braces,  and  the  whole  mass  of 
scale  and  dirt  must  be  swept  down  through  the  water-spaces  to  the  bottom  of  the 
boiler,  taking  special  care  that  no  dirt  lodges  between  the  tubes  or  on  the  furnace- 
crowns.  The  dirt  is  then  raked  with  small  hoes  out  of  the  boiler  through  the  mudholes 
in  the  bottom. 

Finally  the  boiler  is  to  be  washed  out.  By  means  of  a  hose,  connected  to  a  force- 
pump,  direct  a  heavy  stream  of  water  at  every  portion  of  the  interior  of  the  boiler, 
especially  at  such  parts  as  are  not  accessible  for  scraping.  By  this  means  much  loose 


402  STEAM  BOILERS.  CHAP.  XVII. 

scale  and  mud  will  be  washed  down.  The  latter  contains  frequently  grease,  partly  de- 
composed, various  salts,  particles  of  copper,  and  other  substances  which  are  very  inju- 
rious to  the  boiler.  Commence  the  washing-out  in  the  steam-space,  directing  the  jet  of 
water  especially  into  the  steam-drum,  between  the  tubes,  and  into  the  water-spaces 
around  the  back-connections.  Then  take  the  hose  in  succession  into  each  manhole  over 
the  furnace-crowns,  and  finally  into  the  mudholes  at  the  bottom  ;  commencing  at  one 
end  of  the  boiler,  wash  all  the  dirt  to  the  other  end.  During  this  operation  continue 
to  rake  the  dirt  and  scale  out  through  the  mudholes  in  the  bottom.  Give  a  slight  list 
to  the  vessel  while  washing  out  the  boilers,  so  that  the  water  will  naturally  flow  to  the 
front  of  the  boilers,  carrying  the  dirt  along  with  it.  The  fire-room  floor-plates  in  front 
of  the  boiler  are  removed  to  let  the  water  run  directly  into  the  bilge  of  the  vessel. 

After  the  boiler  has  been  washed  out,  and  all  the  water  removed  from  the  bottom  by 
raking  and  swabbing,  the  boiler  must  be  kept  open  till  it  is  perfectly  dry  in  every  part. 
Pans  with  burning  charcoal  may  be  placed  in  the  furnaces  and  connections  to  dry  the 
boiler  more  rapidly.  (See  section  14  of  the  present  chapter.') 

13.  Repairing  Boilers. — All  leaks,  however  small,  should  be  stopped  as  soon  as 
possible,  and  all  temporary  repairs,  such  as  have  been  described  in  section  3  of  the  pre- 
sent chapter,  should  be  replaced,  after  the  boilers  are  emptied,  by  substantial  work 
which  will  correct  the  evil  permanently  and  strengthen  the  defective  part.  The  mass 
of  steam  evolved  from  a  leak  frequently  prevents  its  exact  location  while  the  boiler  is 
under  steam,  and  the  accumulation  of  salt  deposited  by  the  water  issuing  from  a  leak 
is  often  so  great  that  its  source  cannot  be  traced  after  the  boiler  is  emptied,  except  by 
filling  it  again  with  cold  water  and  producing  a  pressure  in  it  by  means  of  a  force- 
pump. 

Leaky  seams  and  rivets  must  be  calked.  When  a  rivet  leaks  after  repeated  calking 
it  must  be  cut  o\it  and  a  new  rivet  put  in  its  place.  The  same  must  be  done  with  rivets 
the  heads  of  which  are  so  much  corroded  that  their  holding  power  is  seriously  impaired. 
Such  rivet-heads  are  found  especially  at  the  bottom  of  boilers  on  the  outside  of  the 
shell  and  in  the  connections  and  uptakes,  and  their  condition  is  frequently  not  indi- 
cated by  any  leaks,  and  may  not  be  discovered,  since  the  corroded  heads  often  retain 
their  original  shape,  unless  they  are  tested  by  striking  them  with  a  hammer.  In  places 
where  new  rivets  cannot  be  driven  properly  bolts  secured  by  nuts  may  be  substituted 
for  them.  To  make  a  tight  joint  with  them  wrap  a  little  hemp  or  cotton  wick  covered 
with  putty  around  their  shank  close  under  the  head,  and  put  a  washer  covered  with 
stiff  putty  under  the  nut.  Such  bolts  must  likewise  be  used  when  the  boiler  is  old  and 
weak,  as  the  jars  produced  by  riveting  and  calking  would  be  likely  to  start  new  leaks. 


SBC.  13.  MANAGEMENT  OP  BOILERS.  403 

These  bolts  have  frequently  to  be  wired  in  place  by  the  same  method  as  is  applied  to 
sockets,  described  in  section  3,  chapter  x. 

In  replacing  a  socket-bolt  keep  the  socket  in  place  by  inserting  the  new  bolt  or  a 
temporary  plug  as  the  old  bolt  or  rivet  is  being  withdrawn.  After  removing  screw  stay- 
bolts  the  threads  in  the  plates  are  generally  found  so  much  injured  that  the  holes  have 
to  be  reamed  out  and  new  threads  cut,  necessitating  the  use  of  larger  bolts.  When  the 
holes  have  become  much  enlarged  or  the  plates  much  weakened  by  corrosion  replace 
socket-rivets  and  screw  stay-bolts  with  socket-bolts,  and  put  large  washers  under  their 
heads  and  nuts. 

Defective  parts  of  a  boiler  have  often  to  be  patched  with  plate-iron,  in  order  to 
strengthen  them  or  to  stop  leaks. 

When  a  patch  is  riveted  on  and  made  tight  by  calking  it  is  called  a  hard  patch. 
When  a  patch  is  bolted  over  the  defective  place,  the  joint  being  made  with  putty,  it  is 
called  a  soft  patch.  The  bolts  are  generally  secured  by  nuts,  but  sometimes  tap-bolts 
have  to  be  used.  The  putty  is  prepared  by  kneading  together  white  lead,  ground  in  oil, 
with  dry  red  lead,  and  mixing  with  it  some  fine  iron  borings  or  filings  to  make  it  stiff. 

A  soft  patch  should  not  be  applied  to  a  surface  in  contact  with  fire  or  hot  gases, 
except  in  case  of  necessity  as  a  temporary  expedient  to  stop  a  bad  leak.  When  a  soft 
patch  has  been  applied  to  a  furnace-crown  it  is  best  not  to  use  the  furnace,  because  the 
heat  would  cause  the  patch  to  warp  sooner  or  later.  On  the  bridge-wall  or  on  the  bot- 
tom of  the  back-connection  a  soft  patch  may  be  protected  by  covering  it  with  fire-clay  or 
ashes.  When  a  boiler  is  old  and  weak  a  soft  patch  is  often  to  be  preferred  to  a  hard 
patch  to  avoid  jarring  the  boiler  by  riveting  and  calking.  Leaky  seams  which  have 
been  repeatedly  calked,  so  that  the  lap  is  much  reduced  in  width,  have  to  be  made  tight 
by  covering  them  with  a  soft  patch.  It  must  be  observed  that  a  soft  patch  generally 
does  not  add  to  the  strength  of  the  defective  plate,  but  is  frequently  the  cause  of  greater 
weakness  on  account  of  the  metal  cut  away  in  drilling  the  bolt-holes,  and  because  corro- 
sion may  continue  unseen  under  the  patch. 

When  a  hard  patch  is  to  be  applied  to  the  outer  shell  it  may  be  placed  directly  over 
the  defective  plate.  But  in  places  which  come  in  contact  with  the  fire  or  hot  gases  it  is 
necessary  to  reduce  the  thickness  of  the  metal  as  much  as  possible  ;  therefore  the  defec- 
tive part  has  to  be  cut  out.  The  hole  thus  formed  in  the  plate  should  be  rounded,  since 
sharp  corners  favor  the  formation  of  cracks. 

Cut  the  patch  from  boiler-plate  of  good  quality  and  of  the  same  thickness  as  the 
plate  which  is  to  be  repaired,  unless  the  latter  is  much  worn,  when  the  patch  may  be 
reduced  in  thickness.  It  is  advisable  to  calk  the  edges  of  the  patch  rather  than  those  oi 


404  STEAM  BOILERS.  CHAP.  XVII. 

the  old  plate  ;  for  this  reason,  in  repairing  a  crown-sheet,  put  the  patch  inside  the  fur- 
nace ;  in  this  position  it  can  also  be  fitted  better  than  when  it  is  placed  inside  the  boiler. 
After  cutting  away  the  defective  portion  of  the  plate  with  a  cape-chisel,  lay  off  and  drill 
around  the  opening  rivet-holes  of  the  required  size  and  spaced  according  to  the  rules 
given  in  sections  13  and  14,  chapter  viii.  Pit  the  patch  so  that  it  lies  close  on  the  plate, 
and,  holding  it  in  position,  mark  on  it  the  rivet-holes  and  the  opening  cut  in  the  plate. 
Then  drill  the  holes  and  trim  the  patch  to  the  proper  size  and  form.  Bolt  it  securely  in 
place  while  it  is  being  riveted,  and  finally  calk  it. 

When  the  patch  is  to  cover  a  curved  or  uneven  surface  make  a  template  for  it  of  a 
piece  of  sheet-lead  hammered  into  shape  while  holding  it  against  the  surface  to  be  cov- 
ered. After  fitting  and  drilling  the  patch  heat  it  to  a  dull-red  heat,  put  it  in  position, 
and  draw  it  tight  up  against  the  plate  by  means  of  bolts,  so  as  to  make  a  close  fit. 

Blisters  occur  frequently  in  iron  plates  exposed  to  an  intense  heat.  When  they  are 
thin  it  is  sufficient  to  chip  them  off  as  far  as  the  lamination  extends  ;  but  when  a  blister 
is  thick  the  plate  has  to  be  cut  out  and  patched.  Some  engineers  recommend  to  rivet 
blisters  down  when  they  first  appear,  and  thus  prevent  their  extension. 

Cracks  formed  by  unequal  expansion  in  the  middle  of  plates,  or  starting  from  rivet- 
holes,  are  sure  to  increase  in  length  unless  promptly  stopped.  When  a  crack  does  not 
exceed  three  inches  in  length  it  may  be  closed  with  rivets.  Drill  a  small  hole  at  each 
end  of  the  crack,  taking  care  that  it  does  not  extend  beyond  the  holes,  then  drill  one  or 
two  more  holes  through  the  crack  and  countersink  them.  Put  rivets  through  these 
holes  and  spread  their  heads  well,  hammering  them  down  pretty  flat  so  that  they  cover 
the  crack  completely. 

When  the  crack  is  of  considerable  length  the  corresponding  portion  of  the  plate 
must  be  cut  away  and  patched.  The  same  must  be  done  when  cracks  run  from  hole 
to  hole  in  a  seam,  or  when  a  number  of  cracks  appear  in  close  vicinity,  running  from 
the  rivet-holes  of  a  seam  to  the  edge  of  the  plate. 

When  a  furnace-crown  has  come  down,  or  partly  collapsed,  but  the  injury  is  not  very 
extensive,  it  may  be  restored  to  its  original  shape.  Bring  the  defective  place  to  a  dull- 
red  heat  by  means  of  a  charcoal-fire  in  a  portable  furnace,  then  force  it  up  with  a  screw- 
jack,  placed  on  a  foundation  of  blocks  in  the  ashpit,  and  acting  directly  on  a  block  the 
upper  surface  of  which  has  the  shape  of  the  furnace-crown.  The  adjoining  unin- 
jured parts  of  the  crown-sheet  should  be  firmly  wedged  to  prevent  their  distortion  dur- 
ing this  operation.  It  is  to  be  observed  that  the  injured  part  never  regains  its  original 
strength  and  stiffness.  It  may  be  strengthened  by  additional  braces,  or  by  angle-iron 
rings,  as  described  in  section  6,  chapter  ix.  The  safest  plan  is  to  renew  the  plate,  either 


SEC.  13.  MANAGEMENT  OP  BOILERS.  405 

in  part  or  wholly,  according  to  the  extent  of  the  injury.  When  these  precautions  can- 
not be  taken  before  the  boiler  has  to  be  used  again,  the  defective  furnace  may  be  put 
out  of  use  and  the  injured  crown-sheet  shored  up. 

When  a  crown-sheet  is  defective  in  several  places  it  is  better  to  cut  out  the  whole 
plate,  or  at  least  the  portion  containing  the  several  defects,  than  to  put  on  a  number  of 
small  patches.  Arrange  the  patches  so  that  their  seams  do  not  come  close  to  the  fire, 
and  that  they  clear  the  crow-feet  and  other  attachments  of  the  braces. 

When  tubes  leak  in  the  joints  at  their  ends,  and  cannot  be  made  tight  by  expanding 
or  calking  them,  the  leak  may  be  stopped  by  driving  ferrules  in  their  ends.  Several 
methods  of  plugging  fire-tubes  have  been  described  in  section  3  of  the  present  chapter. 
On  account  of  the  expansion  of  the  rod  exposed  to  the  hot  gases,  water-tubes  cannot  be 
plugged  effectually  in  the  same  manner  as  fire-tubes  by  passing  through  them  a  long 
rod  with  a  nut  at  each  end  which  holds  the  cup- washers  that  cover  the  ends  of  the  tube. 
Such  tubes  must  be  cut  out,  and  the  holes  in  the  tube-sheets  must  be  closed  by  cup- 
washers,  each  held  by  a  short  bolt  having  a  T-head  or  passing  through  an  iron  bar 
which  straddles  the  tube-hole.  Tubes  which  have  been  plugged  should  be  replaced  as 
soon  as  possible  with  new  ones.  The  manner  of  securing  tubes  has  been  described  in 
section  6,  chapter  xi. 

To  remove  a  ferrule  from  a  tube  split  it  by  cutting  a  groove  through  it  with  a  cape- 
chisel.  A  tube  in  one  of  the  outside  rows  may  be  removed  by  cutting  it  off  with  a  tube- 
cutter  or  with  a  chisel  inside  the  tube-sheets.  To  remove  a  tube  from  one  of  the  inner 
rows  bend  its  ends  inward,  pass  a  rod  through  it,  and  put  a  nut  and  washer  at  one  end  ; 
hook  a  tackle  at  the  other  end  and  pull  the  tube  out,  driving  it  at  the  same  time  at  the 
other  end.  The  accumulation  of  scale  on  a  tube  makes  its  passage  through  the  hole  in 
the  tube-plate  often  very  difficult.  The  scale  may  be  cracked  off  by  inserting  a  red-hot 
iron  bar  into  the  tube.  Tubes  which  have  been  removed  can  often  be  used  again  in 
shorter  boilers  after  cutting  off  their  battered  ends,  or  they  may  be  lengthened  by  braz- 
ing new  ends  to  them. 

If  a  tube-plate  is  bulged  from  any  cause,  tie  it  to  the  opposite  tube-plate  by  means 
of  rod-braces  which  take  the  place  of  some  of  the  tubes,  and  are  held  at  the  ends  by 
nuts  and  stout  washers,  or  substitute  stay-tubes  secured  by  nuts  for  a  number  of  tubes 
expanded  in  the  ordinary  manner. 

Leaky  seams  of  old  boilers  which  cannot  be  calked  properly  may  be  made  tight  by 
driving  an  iron  cement  into  them,  forming  a  rust- joint.  The  following  composition  for 
such  a  cement  is  given  by  Roper :  cast-iron  borings  or  turnings,  19  Ibs. ;  pulverized 
sal-ammoniac,  1  Ib. ;  flour  of  sulphur,  £  Ib. ;  should  be  thoroughly  mixed  and  passed 


406  STEAM  BOILERS.  CHAP.  XVII. 

through  a  tolerably  fine  sieve.  Sufficient  water  should  be  added  to  wet  the  mixture 
through.  It  should  be  prepared  some  hours  before  being  used.  A  small  quantity  of 
sludge  from  the  trough  of  a  grindstone  will  improve  its  quality.  Instead  of  sal-am- 
moniac, urine  may  be  used. 

When  a  boiler  is  old  and  much  worn  leaks  in  seams,  around  rivet  and  stay-bolt 
heads,  and  at  the  ends  of  tubes  frequently  become  very  general.  When  time  is  want- 
ing to  subject  the  boiler  to  thorough  repairs  the  leaks  may  frequently  be  stopped  tem- 
porarily by  introducing  into  the  boiler  oatmeal,  or  some  other  substance  which  is 
changed  into  a  paste  by  boiling,  and,  after  steam  is  formed,  finds  its  way  into  every 
crevice  or  point  of  least  resistance.  The  presence  of  such  substances  in  the  boiler  pro- 
duces, however,  generally  violent  foaming,  and  they  often  obstruct  the  passages  of 
water-gauges  and  clog  the  valve-seats. 

When  the  water-legs  and  bottoms  of  old  boilers  are  worn  out  generally,  so  that  they 
can  no  longer  be  made  tight  by  calking  and  patching,  they  may  be  filled  with  cement. 
Level  the  boiler  by  trimming  ship  till  a  little  water  in  the  boiler  stands  at  the  same  depth 
everywhere.  Close  the  mudhole-doors.  Prepare  a  mixture  of  three  parts  of  Portland 
cement  and  one  of  sand,  or  equal  parts  of  Roman  cement  and  sand,  with  water,  thin 
enough  to  ran,  in  a  trough  placed  in  the  fire-room  at  a  height  slightly  above  the  man- 
holes between  the  crown-sheets.  An  inclined  shoot  leads  from  this  trough  to  each  man- 
hole. The  cement  must  be  mixed  in  the  trough  in  sufficient  quantity  at  once  and  with 
some  quickness,  as  it  sets  rapidly  under  water.  The  level  of  the  cement  in  the  boiler 
must  be  kept  some  inches  below  the  grate-bars,  and  the  extremities  of  the  feed  and 
blow  pipes  must  be  kept  clear. 

14.  Preservation  of  Boilers.— A  proper  observance  of  the  rules  for  the  manage- 
ment of  boilers  given  in  the  present  chapter  is  essential  for  their  preservation.  The 
action  of  the  various  causes  tending  to  deteriorate  steam  boilers,  and  the  means  by 
which  their  influences  may  be  neutralized,  will  be  described  in  detail  in  the  following 
chapter. 

The  most  efficient  method  of  protecting  a  boiler  against  internal  corrosion  consists 
in  covering  its  surfaces  with  a  thin,  adhesive  layer  of  ordinary  boiler-scale.  This  scale 
must  be  formed  as  soon  as  possible  after  steam  is  raised,  before  oxidation  has  com- 
menced on  the  iron  surfaces  :  and  it  must  be  very  thin,  otherwise  it  will  soon  crack  with 
the  expansions  and  contractions  of  the  plates,  and  the  moisture  entering  and  retained 
between  the  iron  and  the  scale  will  aggravate  the  evil  of  corrosion.  It  is  recommended 
to  keep  the  water  in  the  boiler  at  about  tJtree  times  the  density  of  ordinary  sea-water 
for  a  short  time  after  steam  is  raised,  in  order  to  produce  this  protective  layer  of  scale. 


SBC.  14.  MANAGEMENT  OF  BOILERS.  407 

In  England  a  thin  coating  of  Portland  cement  has  sometimes  been  substituted  for 
scale  on  the  interior  surfaces  of  boilers.  It  is  recommended  that  all  boilers  under  con- 
struction should  receive  such  a  coating,  which  should  be  renewed  after  the  boiler  has 
been  tried  under  steam.  The  cement  is  ground  very  fine,  and  two  parts  of  cement  are 
mixed  with  one  part  of  sand.  Before  applying  it  the  iron  should  be  scraped  quite  bare, 
otherwise  the  cement  will  not  adhere  to  it.  It  is  then  applied  with  a  common  white- 
wash-brash like  paint ;  as  soon  as  one  coat  is  dry  another  is  laid  on,  two  or  three  coats 
being  applied  in  this  manner.  The  cement  becomes  quite  hard,  almost  like  iron  ;  the 
thinner  it  is  applied  the  better,  otherwise  the  expansion  and  contraction  of  the  plates 
will  throw  it  off.  In  some  cases  it  has  been  found  to  stick  upon  the  sides  and  tops  of 
furnaces  for  two  or  three  voyages.  It  is  recommended  to  fill  with  it  the  holes  caused  by 
pitting,  after  scraping  the  respective  parts  quite  clean.  It  is  sometimes  used  as  a  foun- 
dation upon  which  a  firmly-adhering  layer  of  ordinary  scale  is  allowed  to  accumulate. 
When  it  is  properly  applied  it  is  not  washed  off  by  the  feed,  but  on  the  Sultan  and 
Olatton  its  use  was  discontinued  because  particles  of  it  were  carried  over  into  the 
engines  ;  this  is  ascribed  to  the  faulty  manner  in  which  it  was  applied.  Sometimes  a 
layer  of  cement  about  1  inch  thick  is  applied  to  the  bottom  of  cylindrical  boilers  in- 
side to  protect  them  against  corrosion. 

To  prevent  the  corrosion  of  boilers  when  not  in  use  they  must  be  kept  dry,  and  the 
iron  must  be  covered  inside  and  outside  with  a  protective  coating.  Every  part  of  the 
boiler  should  receive,  when  new,  one  or  two  coats  of  metallic  paint.  Boilers  that  are  to 
be  laid  up  for  some  length  of  time  receive  often  inside  a  coat  of  oil,  which  is  applied 
with  a  syringe  at  parts  which  cannot  be  reached  with  a  brush.  Fish-oil  was  formerly 
frequently  used  for  United  States  naval  boilers,  but  its  use  is  now  interdicted  and 
hydrocarbon  oils  are  to  be  used  instead,  because  their  decomposition  is  not  accompanied 
by  the  formation  of  fatty  acids.  Boilers  built  for  the  English  naval  service  have  been 
completely  filled  with  linseed  or  mineral  oil.  A  pressure  of  15  or  20  pounds  was  pro- 
duced by  means  of  a  force-pump,  provision  being  made  for  the  escape  of  air  from  the 
upper  corners  of  the  boiler ;  the  oil  was  then  run  out,  and  the  process  was  renewed  every 
six  months.  In  other  cases  the  boilers  have  been  heated  gently  to  dry  them,  and  two 
coats  of  boiled  linseed-oil  have  been  applied.  In  all  such  cases  the  surfaces  must  be 
carefully  cleaned  of  rust  and  loose  scale  before  the  oil  is  applied  to  them. 

In  the  English  navy  two  different  systems  are  used  for  the  preservation  of  boilers  not 
in  use.  The  one  is  known  as  the  wet  and  the  other  as  the  dry  system.  The  former  con- 
sists in  keeping  the  boilers  filled  completely  with  sea-water  mixed  with  carbonate  of 
soda ;  25  pounds  if  soda-ash,  or  50  pounds  if  ordinary  crystal-soda,  be  used  for  every 


408  STEAM  BOILERS.  CHAP.  XVII. 

100  cubic  feet  of  sea- water  in  the  boiler.  This  is  to  be  dissolved  and  placed  in  the  bot- 
tom before  running  up  the  boiler.  The  sufficient  saturation  of  the  water  with  soda 
should  be  tested  by  placing  a  piece  of  clean,  new  iron  with  some  of  the  mixture  in  a 
bottle  for  a  night ;  if  the  iron  rusts  more  soda  must  be  added.  Special  care  must  be 
taken  that  every  part  of  the  boiler  is  filled,  the  air  being  allowed  to  escape  from  the 
highest  part  of  the  boiler. 

Instead  of  soda,  slaked  lime  is  also  used,  in  the  proportion  of  8  pounds  of  lime  to 
every  1,000  gallons  of  sea- water.  This  lime  must  be  carefully  cleaned  out  before  getting 
up  steam,  or  there  may  be  heavy  priming. 

The  dry  process  consists  iu  removing  all  water  from  the  boilers  to  dryness,  by  means 
of  stoves  if  necessary  ;  after  which  shallow  iron  pans  containing  altogether  two  or  three 
hundred-weight  of  quicklime  are  placed  in  the  bottoms,  over  the  furnaces,  and  above 
the  tubes,  the  quantity  of  lime  depending  on  the  size  of  the  boiler.  In  addition  a  sheet- 
iron  tray  of  burning  coal  is  to  be  placed  in  the  ashpits  or  furnaces  till  the  coal  is  coked ; 
then  it  is  introduced  into  the  boiler  and  the  latter  immediately  closed  air-tight.  The  burn- 
ing coke  consumes  much  of  the  oxygen  of  the  air  in  the  boiler,  and  increases  the  effi- 
ciency of  the  dry  lime.  At  least  every  six  months  the  boiler  is  to  be  opened  for  inspec- 
tion, and,  if  the  lime  is  found  to  be  much  slaked,  the  pans  at  the  bottom,  which  can  be 
removed  without  considerably  changing  the  air,  are  to  be  taken  out  and  refilled  with 
fresh  lime.  In  addition  to  this,  when  the  atmospheric  dampness  is  extreme,  light  fires 
in  the  ashpits  are  sometimes  found  to  be  necessary. 

Weston  found  that  the  amount  of  oxygen  lost  by  the  air  in  boilers  where  the  dry 
process  had  been  used  varied  from  nothing  (in  two  cases)  to  90  per  cent.  The  dry -lime 
process  frequently  fails  from  the  extreme  difficulty  of  absolutely  excluding  moisture. 
By  introducing  the  burning  coke  into  the  boiler  60  per  cent,  of  the  oxygen  in  the 
boiler  may  be  consumed  at  once.  After  opening  a  boiler  which  has  been  treated 
by  the  dry-lime  process,  air  must  be  allowed  to  circulate  through  it  before  any  one 
enters  it. 

15.  Extract  from  "Instructions  for  the  Care  and  Preservation  of  the 
Steam-machinery  of  United  States  Naval  Vessels  (1879)." 

"16.  A  thin  deposit  of  scale  will  be  useful  in  protecting  the  interior  surfaces  of  boil- 
ers from  corrosive  action,  and  the  use  of  zinc  in  the  boilers  will,  it  is  believed,  divert 
corrosion  from  the  iron.  In  order  that  the  best  results  may  be  obtained  it  is  deemed 
advisable  to  ensure  metallic  continuity  between  the  zinc  and  the  boilers. 

"17.  No  tallow  or  oil  of  vegetable  or  animal  origin  is  to  be  put  into  the  boilers  for 
any  purpose  whatever,  but  Cranes  mineral  oil,  or  its  equivalent,  will  be  used.  This 


SEC.  15.  MANAGEMENT  OF  BOILERS.  409 

prohibition  applies  to  all  boilers  in  nse  in  the  navy  under  cognizance  of  this  Bureau,  of 
whatever  type  or  service. 

"18.  The  dry-pipes  and  drains  of  the  steam-drums  are  to  be  examined  frequently 
to  ascertain  if  the  holes  in  them  are  clear. 

"19.  The  boilers,  when  empty,  are  to  be  kept  dry  by  such  means  as  are  at  the  dis- 
posal of  the  officer  in  charge.  The  water-bottoms  and  lower  parts  of  the  fronts  are  to  be 
kept  free  from  scale,  rust,  and  ashes,  and  well  painted. 

"20.  The  boilers  are  not  to  be  used  as  water- tanks  for  fresh  water,  nor  for  trimming 
ship. 

"21.  The  exteriors  are  to  be  kept  as  dry  as  possible,  and  nothing  wet  or  com- 
bustible is  to  be  stowed  over  or  around  them.  The  bilges  in  the  fire-room  are  to  be 
kept  dry  and  well  whitewashed. 

"22.  Sudden  changes  of  temperature  in  the  boilers  are  to  be  avoided,  and,  when 
time  will  permit,  at  least  three  hours  should  be  occupied  in  raising  steam  from  cold 
water. 

"23.  When  not  under  steam  a  cover  must  be  fitted  to  prevent  water  from  going 
down  the  smoke-pipe. 

"  24.  The  uptakes  are  to  be  kept  free  from  dirt  and  well  painted. 

"  25.  The  number  of  hours  each  boiler  has  had  fires  within  it  since  the  ship  was  com- 
missioned is  to  be  stated  in  each  quarterly  report. 

"26.  After  the  fires  are  hauled,  and  before  the  water  is  blown  out  of  the  boilers,  the 
furnaces  and  ashpits  should  be  closed. 

"27.  The  mineral  oils  which  are  to  be  used  for  interior  lubrication  float  on  the  sur- 
face of  the  water  in  the  boilers  without  being  decomposed,  and  the  surface-blows  are  to 
be  used  as  rarely  as  possible,  in  order  that  the  oil  may  not  be  blown  overboard." 


CHAPTER  XYIII. 

CAUSES  AND   PREVENTION   OF  THE   DETERIORATION   OF  BOILERS. 

1.  General  Causes  of  the  Deterioration  of  Boilers. — The  deterioration  of 
boilers  consists  in  the  accumulation  of  calcareous  scale  and  sediment  within  them,  and 
in  the  diminution  of  their  strength  and  the  starting  of  leaks  in  consequence  of  corrosion 
and  fracture  and  of  the  burning  and  distortion  of  the  plates. 

The  deterioration  of  boilers  is  due  to  a  variety  of  known  causes,  many  of  which  are 
in  a  great  measure  avoidable,  while  for  some  of  them  no  reliable  practicable  method  of 
prevention  has  yet  been  discovered.  There  are  some  destructive  agencies  at  work,  short- 
ening the  life  of  boilers,  the  action  of  which  is  not  fully  understood  ;  and  instances  of 
rapid  deterioration  of  boilers  occur  from  time  to  time  for  which  no  definite  cause  can  be 
assigned.  In  general  the  untimely  deterioration  of  boilers  may  be  traced  to  some  of  the 
following  causes — viz. : 

Inferior  quality  of  or  defects  in  the  materials  used  in  the  construction  of  the  boilers, 
especially  the  want  of  strength  and  ductility,  and  the  presence  of  cracks,  laminations, 
and  surface-defects  in  plates. 

Bad  workmanship,  causing  injuries  to  the  materials  by  punching,  drifting,  and  burn- 
ing, indenting  the  plates  in  calking,  defective  welding  and  riveting,  and  want  of  tight- 
ness in  seams. 

Deficiency  of  structural  strength  of  the  boiler  and  improper  methods  of  connecting 
the  various  parts,  causing  severe  local  strains  to  be  produced  by  the  steam-pressure 
or  by  the  unequal  expansion  and  contraction  of  certain  parts  in  consequence  of  varia- 
tions of  temperature. 

Faulty  design  of  the  boiler,  causing  inaccessibility  for  cleaning  and  repairs,  and 
defective  circulation  of  the  water  preventing  the  free  escape  of  steam  from  heating- 
surfaces. 

Mismanagement  of  the  boiler :  subjecting  it  to  great  differences  and  sudden  variations 
of  temperature ;  overheating  the  parts  exposed  to  the  direct  action  of  the  fire  or  hot 
gases  ;  letting  the  steam-pressure  exceed  the  safe  limit ;  allowing  the  formation  of  thick 
deposits  of  scale,  and  neglecting  to  clean  and  repair  the  boiler  in  time,  to  keep  it  dry,  to 
protect  the  surfaces  by  paint,  etc. 

410 


SEC.  1.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OF  BOILERS.  411 

The  use  of  sulphurous  fuel  and  of  impure  feed- water  containing  corrosive  substances 
and  producing  deposits  of  solid  matter. 

Galvanic  action  in  consequence  of  the  presence  of  heterogeneous  metals  in  the  boiler, 
which  either  enter  in  its  construction  or  have  been  introduced  with  the  feed- water. 

A  gradual  deterioration  of  boilers  after  they  have  been  put  in  use  appears  unavoid- 
able ;  but  while  stationary  boilers  frequently  last  twenty  years,  the  life  of  marine  boilers 
ranges,  under  favorable  conditions,  from  nine  to  twelve  years,  and  in  naval  vessels  is 
often  limited  to  six  years  of  use. 

The  greater  durability  of  stationary  boilers  compared  with  that  of  marine  boilers  is 
mainly  owing  to  two  circumstances.  In  the  first  place,  stationary  boilers  can  generally 
be  made  of  such  a  size  and  capacity  that  there  is  no  need  of  urging  the  fires,  and  of  such 
a  form  that  they  are  accessible  in  every  part,  that  the  circulation  of  the  water  and  the 
escape  of  the  steam  from  their  heating-surfaces  is  unobstructed,  and  that  the  alterations 
of  form  due  to  variations  of  pressure  and  temperature  do  not  produce  severe  local 
strains  ;  while  in  marine  boilers  these  conditions  have  frequently  to  be  sacrificed  on  ac- 
count of  the  restrictions  with  regard  to  weight  and  space  imposed  upon  the  designer. 
In  the  second  place,  the  feed- water  of  stationary  boilers  is  generally  purer  than  that  of 
marine  boilers,  since  the  water  used  for  the  purpose  is  either  originally  more  free  from 
injurious  salts  and  acids,  or  can  be  passed  through  purifiers  of  ample  capacity  which 
would  not  be  permissible  on  board  of  vessels  on  account  of  their  bulk  and  weight. 

A  perceptible  diminution  of  the  endurance  of  marine  boilers  has  taken  place  since 
the  introduction  of  surface-condensers  and  of  high  steam-pressures. 

The  shorter  life  of  boilers  in  naval  vessels  compared  with  that  of  boilers  in  merchant- 
vessels  is  to  be  ascribed  principally  to  the  irregular  manner  in  which  the  former  have 
often  to  be  worked.  The  boilers  of  merchant- vessels  are  generally  worked  under  uni- 
form conditions  for  regular  periods,  with  certain  intervals  of  rest  during  which  the  boilers 
may  be  cleaned  and  repaired.  On  the  other  hand,  in  boilers  of  naval  vessels  steam  has 
frequently  to  be  raised  very  quickly.  They  are  sometimes  kept  under  steam  for  long 
periods,  either  working  with  full  power  or  lying  under  banked  fires  ;  and  at  other  times 
steam  is  raised  and  lowered,  and  the  fires  are  started  and  hauled,  after  short  intervals. 
Under  these  conditions  the  boilers  of  naval  vessels  are  subjected  to  frequent  changes  and 
inequalities  of  temperature,  and  to  frequent  exposure  of  their  imperfectly-dried  surfaces 
to  the  action  of  the  atmospheric  air ;  their  cleaning  and  repairs  cannot  take  place  at 
regular  intervals,  and  the  facilities  for  effecting  thorough  repairs  are  frequently  wanting 
during  long  cruises  on  distant  stations. 

The  formation  of  thick  deposits  of  scale  on  the  heating-surfaces  of  boilers  not  only 


412  STEAM  BOILERS.  CHAP.  XVIII 

diminishes  greatly  their  evaporative  efficiency,  bnt  leads  frequently  to  injuries  affecting 
their  strength  and  durability  by  causing  the  plates  to  become  overheated.  The  condi- 
tions under  which  scale  is  formed,  its  character,  and  the  method  of  preventing  its  forma- 
tion by  blowing-off  have  been  discussed  in  sections  5-10,  chapter  xvii.  Various  other 
means  of  preventing  its  formation  will  be  discussed  in  sections  10  and  11  of  the  present 
chapter. 

The  external  corrosion  of  the  shell  of  marine  boilers — caused  by  leakage  from  seams, 
rivets,  man  and  hand  holes,  water-gauges,  etc.,  the  leakage  of  water  through  the  deck, 
and  the  action  of  the  bilge-water  and  of  wet  ashes  on  the  bottom  and  front  of  boilers — is 
easily  prevented  by  stopping  promptly  all  leaks,  keeping  the  surfaces  of  the  boiler 
clean,  and  protecting  it  with  a  coat  of  paint.  (See  section  12,  chapter  xvii.)  The  sup- 
ports on  which  the  boiler  rests  must  be  arranged  in  such  a  manner  that  the  bottom  of 
the  boiler  is  easily  accessible.  External  corrosion  will  also  take  place  when  boilers 
rest  directly  on  oaken  keelsons,  or  when  copper  bolts  are  allowed  to  come  in  contact 
with  the  iron  of  the  shell  of  boilers.  (See  section  1,  chapter  xiv.) 

The  deterioration  of  the  plates  forming  the  heating-surfaces  of  boilers,  produced  by 
overheating,  variations  and  differences  of  temperature,  the  corrosive  action  of  the  gases 
of  combustion  and  of  sulphuric  acid  distilled  from  soot,  and  the  various  causes  of  the 
internal  corrosion  of  boilers,  will  be  discussed  separately  in  the  following  sections  of  the 
present  chapter.  Many  of  the  causes  of  the  deterioration  of  boilers  may  be  prevented 
by  observing  the  directions  for  the  management  of  boilers  given  in  chapter  xvii.  The 
internal  corrosion  of  boilers  is  mainly  due  to  the  exposure  of  their  damp  surfaces  to  the 
atmospheric  air,  the  presence  of  chloride  of  magnesium  and  of  fatty  acids  in  the  feed- 
water,  and  the  galvanic  action  of  heterogeneous  metals  and  especially  of  particles  of 
copper,  introduced  with  the  feed-water,  in  contact  with  iron. 

In  some  parts  of  the  boiler  the  iron  plates  may  be  raised  to  a  sufficiently  high  tem- 
perature to  decompose  the  steam  in  contact  with  them,  the  oxygen  combining  with  the 
iron  and  forming,  according  to  circumstances,  some  one  of  the  oxides  of  iron.  There 
seems  to  be  no  doubt  that  this  action  frequently  takes  place  in  the  uptake  and  in 
superheaters,  in  which  places  the  corrosion  of  the  iron  plates  generally  presents  a  very 
different  appearance  from  what  it  does  at  other  parts  of  the  boiler.  Professor  Hoff- 
man concludes  from  direct  experiments  that  the  temperature  of  the  iron  has  to  ex- 
ceed 356°  Fahr.  before  decomposition  of  pure  water  takes  place ;  and  Professor  Barff 
states  that  at  a  temperature  of  650°  Fahr.  the  black  oxide  of  iron  will  be  formed  when 
iron  is  exposed  to  the  action  of  superheated  steam. 

The  question  whether  wrought-iron  or  steel  is  more  liable  to  corrosion  has  to  be  con- 


OF    THE 

UNIVERSITY 


SBC.  1.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OP  BOILERS.  413 

sidered  as  remaining  undecided,  the  testimony  in  reference  to  this  point  being  very  con- 
flicting. Steel  plates  having  very  nearly  the  same  chemical  composition,  and  exposed 
in  the  same  boiler  to  apparently  identical  influences,  have  shown  in  some  cases  very  dif- 
ferent results  as  regards  corrosion.  It  is,  however,  generally  believed  at  the  present 
day  that  the  softer  and  purer  kinds  of  steel  and  wrought-iron  are  more  liable  to  cor- 
rosion than  the  harder  and  less  pure  ones. 

Corrosion  does  not  attack  the  surfaces  of  iron  and  steel  plates  in  a  uniform  manner, 
and  this  fact  is  easily  explained  by  the  presence  of  structural  differences  in  the  plates. 
Wrought-iron  and  steel  cannot  have  a  perfectly  homogeneous  structure  from  the  very 
nature  of  the  processes  of  manufacture.  The  former  is  an  aggregation  of  fibres  welded 
together  by  squeezing,  hammering,  and  rolling,  or  separated  by  thin  layers  of  impuri- 
ties ;  steel  ingots  are  known  to  be  traversed  by  innumerable  air  and  gas  cells,  the  walls 
of  which  are  more  or  less  perfectly  welded  together  by  hammering  and  rolling.  A 
highly-polished  plate  of  iron  or  steel  exposed  to  atmospheric  influences  will  show  de- 
tached spots  of  rust  at  first,  which  gradually  enlarge  and  spread  over  the  whole  surface. 
Powerful  acids  attack  different  parts  of  plates  in  a  different  degree,  and  thus  develop 
their  irregular  structure. 

In  steam  boilers,  however,  several  other  circumstances  combine  to  make  corrosive 
action  very  unequal.  At  places  where  the  protective  coating  of  the  black  oxide  of  iron 
or  of  adhesive  scale  has  been  detached  and  the  clean  iron  is  left  exposed,  and  where  the 
fibres  of  the  metal  have  been  loosened  by  bending,  welding,  etc.,  corrosion  will  com- 
mence and  make  the  most  rapid  progress.  Corrosive  substances  may  be  deposited  on 
the  plates  in  detached  masses,  and  thus  exert  a  powerful  action. 

Frequently  the  surfaces  of  plates  exhibit  detached  cavities  of  small  extent,  but  vary- 
ing as  to  depth  from  a  shallow  depression  to  an  actual  perforation  of  the  plate  ;  some- 
times only  a  few  of  these  cavities  lying  far  apart  occur  in  a  plate  ;  at  other  times  they 
lie  so  close  together  that  the  plate  presents  a  honeycombed  appearance.  This  phe- 
nomenon is  called  pitting.  In  the  milder  cases  this  form  of  corrosion  may  have  been 
caused  by  surface-defects  due  to  cinder-spots,  etc.,  but  it  is  probably  more  frequently 
produced  by  the  intense  local  action  of  particles  of  corrosive  substances,  especially  of 
fatty  acids,  or  by  the  galvanic  action  of  particles  of  heterogeneous  metals. 

When  the  plates  exhibit  deep  furrows  following  well-defined  directions  the  phe- 
nomenon is  called  grooving.  These  furrows  are  frequently  found  to  run  at  a  short  dis- 
tance from  and  parallel  to  seams,  and  their  formation  is  explained  by  assuming  that 
the  repeated  bending  of  the  plates  at  these  places  in  alternate  directions  has  gradually 
detached  the  protective  coating  of  scale  and  opened  or  broken  the  fibres  of  the  metal, 


414  STEAM  BOILERS.  CHAP.  XVIII. 

and  has  thus  facilitated  corrosive  action.  Not  unfrequently  such  a  line  of  weakness  is 
produced  by  cutting  into  the  surface  of  the  plate  in  chipping  the  edge  of  the  lap  for  the 
purpose  of  calking  it. 

2.  Deterioration  caused  by  Overheating  and  by  the  corrosive  Action  of 
the  Gases  of  Combustion. — Under  the  influence  of  the  intense  heat  existing  in  the 
furnace  and  combustion-chamber  the  metal  is  liable  to  rapid  oxidation,  especially  in 
laps  and  rivet-heads,  where,  in  consequence  of  the  greater  thickness  of  metal,  the  diffe- 
rence of  temperatures  at  the  water  and  fire  sides  is  relatively  great.  The  metal  is  also 
liable  to  be  destroyed  by  corrosive  gases  given  off  by  the  burning  fuel.  When  sulphu- 
rous fuel  is  burned  the  plates  exposed  to  a  high  temperature  are  acted  upon  with  great 
rapidity,  successive  thin  coats  of  bisulphuret  of  iron  being  formed  on  their  surface. 

In  boilers  worked  with  a  strong  artificial  draught  the  cinders  and  fine  particles  of 
coal  carried  along  by  the  blast  gradually  wear  away  the  metallic  surfaces  against  which 
they  strike.  This  action  has  been  observed  especially  in  locomotives,  where  the  front 
tube-sheet  has  been  found  to  be  much  injured  by  it,  and  where  the  use  of  copper  tubes 
had  to  be  abandoned  on  that  account. 

The  tubes  and  plates  of  superheaters  located  in  the  uptakes  of  boilers  are  liable  to 
become  overheated,  especially  in  starting  the  fires  before  steam  has  formed ;  this  may 
be  prevented  by  filling  them  with  water,  which  is  to  be  drained  off  after  steam  has 
formed  in  the  boiler.  The  upper  part  of  the  front  of  boilers  in  the  uptake  are  exposed 
to  the  same  injury.  The  rules  of  the  Board  of  Trade  (English)  require  that  the  flat 
ends  of  all  boilers,  as  far  as  the  steam-space  extends,  and  the  ends  of  superheaters 
should  be  fitted  with  shield  or  baffle  plates  where  exposed  to  the  hot  gases  in  the 
uptake. 

When  parts  of  the  boiler  exposed  to  an  intense  heat — as  the  furnace-crown,  the  top 
of  the  back-connection  and  horizontal  tubes — are  left  bared  of  water  the  metal  soon  at- 
tains a  red  heat.  Iron  tubes  and  plates  collapse  or  bulge  out  and  warp  when  they  are 
overheated,  and  their  strength  is  frequently  permanently  impaired ;  good,  tough  iron 
becomes  brittle  and  weak  when  it  is  burnt.  Brass  loses  its  strength  and  disintegrates 
at  a  much  lower  temperature  than  that  at  which  iron  is  injured.  Horizontal  fire-tubes 
of  brass  are  quickly  burnt  when  they  are  left  bare  of  water,  but  in  vertical  tubes  the 
water  may  be  carried  far  below  the  upper  tube-plate  without  injuring  them. 

The  overheating  of  furnace-crowns  and  back-connections  is  frequently  caused  by  the 
accumulation  of  scale  or  the  formation  of  a  saponaceous  sediment.  (See  section  4  of  the 
present  chapter.) 

Laminations  existing  in  plates  prevent  the  ready  transmission  of  heat  through  them. 


SEC.  2. 


CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OP  BOILERS. 


415 


When  such  defects  exist  in  plates  forming  the  furnace  or  the  combustion-chamber  the 
layer  in  the  plate  nearest  to  the  fire  becomes  greatly  overheated,  and,  expanding,  bulges 
out.  When  the  extension  of  the  metal  has  exceeded  the  limit  of  elasticity  the  metal 
does  not  resume  its  original  shape  after  the  heat  has  been  discontinued,  and  a  blister  is 
formed,  which  increases  in  size  with  repeated  applications  of  heat,  and  is  sooner  or  later 
fractured,  either  at  the  apex  when  its  thickness  is  uniform,  or  near  the  edge  when  it  is 
thinnest  there. 

When  the  temperature  of  the  plate  exceeds  a  certain  limit  the  phenomenon  of  the 
spheroidal  condition  of  water  is  produced.  According  to  Boutigny,  this  may  take 
place  when  the  temperature  of  an  iron  plate  is  as  low  as  350°  Fahr.  When  the  shape 
or  position  of  the  heating-surface  prevents  the  ready  escape  of  the  steam  from  it,  as  in 
horizontal  water-tubes,  or  when  the  fires  are  urged  much  in  a  boiler  with  defective  cir- 
culation of  the  water,  or  when  the  thick  scale  which  has  accumulated  on  a  heating- 
surface  cracks  and  becomes  detached  by  the  expansion  of  the  overheated  plate,  the  tem- 
perature of  the  latter  may  have  become  high  enough  to  produce  the  spheroidal  condi- 
tion of  the  water ;  and  although  the  repulsion  between  the  water  and  the  plate  may  con- 
tinue only  for  a  few  seconds,  this  time  may  be  sufficient,  with  an  intense  heat,  to  soften 
the  iron  so  that  it  is  forced  outward  by  the  steam-pressure.  In  the  depression  thus 
formed  sediment  is  very  apt  to  lodge  and  accumulate,  favoring  a  repetition  of  the  pro- 
cess, and  by  alternate  heating  and  cooling  this  part  of  the  plate  will  be  either  cracked 
or  burnt  out. 


Relative  tenacity. 

Temperature. 

Experiments  made  by 
committee  of   Franklin 
Institute,  1833-33. 

Experiments  made  by  Kollmann,  1877-78. 

Degrees  Fahr. 

Wro  ught-iron. 

Fibrous 
wrought-iron. 

Fine-grained 
wrought-iron. 

Bessemer  steeL 

32 

100 

IOO 

IOO 

IOO 

212 

.... 

IOO 

IOO 

IOO 

392 

93-8 

95 

IOO 

IOO 

572 

91.7 

90 

97 

94 

932 

66.8 

38 

44 

34 

1292 

30.0 

16 

23 

18 

1652 

•  •  •  • 

6 

12 

9 

I832 

.... 

4 

7 

7 

Experiments  on  the  tenacity  of  wrought-iron  and  steel  at  different  temperatures, 
made  by  Kollmann  in  1877-78,  give  much  lower  results  for  the  tenacity  of  these  metals 
at  temperatures  exceeding  570°  Fahr.  than  the  experiments  made  by  a  committee  of 


416  STEAM  BOILERS.  CHAP.  XVIII. 

the  Franklin  Institute  in  1832-33.  The  foregoing  table,  showing  the  relative  tenacities 
of  wrought-iron  and  steel  at  different  temperatures,  gives  a  brief  summary  of  the  re- 
sults of  these  experiments. 

3.  Strains  produced  by  sudden  Variations  and  great  Differences  of  Tem- 
perature.— If  the  ends  of  a  plate  are  rigidly  fixed  so  that  it  is  incapable  of  altering 
its  length,  while  at  the  same  time  it  cannot  bend  sideways,  an  increase  in  temperature 
of  1°  Fahr.  will  subject  it  to  a  compressive  stress  of  about  150  Ibs.  per  square  inch,  and 
a  decrease  of  1°  Fahr.  will  produce  under  the  same  conditions  a  tensile  stress  of  equal 
intensity  ;  and  these  stresses  are  totally  independent  of  the  sectional  area  of  the  plate. 

When  steel  boiler-plates  were  first  introduced  great  difficulty  was  experienced  from 
the  unequal  expansion  of  plates  which  had  left  the  rolls  at  different  temperatures.  The 
coldest-rolled  plates  expanded  most  on  being  reheated  the  first  time  ;  and,  consequently, 
when  plates  that  had  left  the  rolls  at  different  temperatiares  were  riveted  together  there 
was  a  constant  strain  on  the  joint,  which  often  resulted  in  the  fracture  of  the  plate. 
This  difficulty  was  overcome  by  annealing  all  the  plates  after  they  left  the  rolls. 

The  cracks  which  are  frequently  found  in  the  lap-joints  of  furnaces,  extending  either 
from  the  rivet-holes  to  the  edge  of  the  plate  or  from  hole  to  hole  in  the  seam,  are  pro- 
bably in  most  cases  caused  by  the  unequal  heating  and  sudden  cooling  of  the  plates. 
The  double  thickness  of  plates  at  the  lap  in  contact  with  the  fire  causes  their  tempera- 
ture to  be  greater  than  where  only  a  single  thickness  exists,  and  a  corresponding  ten- 
dency to  expand.  When  a  current  of  cold  air  rushes  in  thrcragh  the  open  furnace-door 
and  impinges  against  the  heated  and  expanded  joint,  it  cools  off  the  outer  plate  sud- 
denly, producing  a  tendency  to  contract.  But  the  inner  plate  of  the  lap  still  retains  its 
original  temperature  and  resists  contraction,  thus  throwing  a  sudden  tensile  strain  on 
the  outside  plate,  which,  if  sufficiently  severe  or  often  repeated,  will  produce  fracture, 
especially  as  the  iron  around  the  rivet-holes  is  frequently  already  injured  by  punching 
or  drifting. 

Long  furnace-flues  should  be  allowed  to  accommodate  themselves  to  the  expansion 
and  contraction  due  to  the  varying  temperatures  either  by  applying  the  Bowling  hoop 
to  them  (see  section  6,  chapter  ix.)  or  by  turning  the  flanges  which  secure  them  with  a 
large  radius.  If  this  is  not  done  they  are  apt  to  crack  through  the  bend  of  the  flanges, 
especially  when  they  are  secured  by  angle-irons,  or  the  end  plates  of  the  boiler  to  which 
they  are  attached  have  to  buckle  with  the  longitudinal  expansion  of  the  flues,  and  the 
constant  repetition  of  this  movement  inevitably  results  in  the  destruction  of  the  plate  ; 
the  more  rigidly  the  plates  are  stayed  the  more  severe  is  this  strain  on  them. 

A  great  difference  of  temperature  exists  often  in  the  upper  and  lower  half  of  furnace- 


SEC.  3.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OF  BOILERS.  417 

flues,  especially  when  the  feed- water  is  cold.  The  resulting  unequal  expansion  throws 
severe  strains  on  the  longitudinal  and  transverse  joints,  besides  weakening  flues  by  dis- 
torting their  circular  cross-section. 

These  strains  are  very  severe  in  the  case  of  the  shell  of  cylindrical  boilers  of  large 
diameter,  the  bottom  of  which  has  the  temperature  of  the  feed-water  while  the  upper 
portions  have  the  temperature  of  the  steam.  The  difference  of  these  temperatures  may 
amount  to  more  than  200°  Fahr.  The  effect  of  these  strains  is  that  the  circumferential 
seams  at  the  bottom  are  frequently  leaky,  while  the  longitudinal  seams  are  generally 
tight.  Many  boilermakers  double-rivet  the  circumferential  joints  on  this  account, 
although  single-riveting  would  be  sufficient  to  resist  the  strains  produced  by  cold-water 
pressure.  In  several  double-end  boilers  these  strains  have  caused  the  fracture  of  the 
plate  between  the  rivet-holes  in  the  circumferential  seams.  On  account  of  these  strains 
the  shell  of  such  boilers  should  be  made  of  a  soft,  ductile  iron.  The  difference  of  tem- 
perature should  be  reduced  as  much  as  possible  by  facilitating  the  circulation  of  the 
water  and  by  increasing  the  temperature  of  the  feed- water. 

The  general  rules  and  regulations  prescribed  by  the  Board  of  Supervising  Inspectors 
of  Steam -vessels  (1879)  provide  that  "the  feed- water  shall  not  be  admitted  into  any 
boiler,  on  board  of  any  steam- vessel  subject  to  the  jurisdiction  of  this  Board,  at  a  less 
temperature  than  one  hundred  (100)  degrees  Fahrenheit  for  low-pressure  boilers,  and 
one  hundred  and  eighty  (180)  degrees  Fahrenheit  for  high-pressure  boilers ;  nor  shall 
cold  water  be  admitted  into  any  such  boiler  while  the  water  is  at  a  less  temperature  than, 
the  sumranding  atmosphere."  Boilers  carrying  a  steam-pressure  exceeding  60  pounds 
to  the  square  inch  are  to  be  considered  as  high-pressure  boilers. 

Plate  XXXVI.  represents  some  specimens  of  rivets  taken  from  the  bottom  of  a  cir- 
cumferential seam  of  an  externally-fired,  cylindrical  flue-boiler,  abont  4  feet  in  diameter. 
The  seam  was  situated  in  the  furnace  near  the  bridge-wall,  and  had  repeatedly  given 
trouble  by  leaking.  The  expansion  and  contraction  of  the  lap  had  evidently  caused  the 
fracture  of  the  rivets,  gradually  detaching  the  conical  heads  from  the  shanks,  so  that 
they  were  held  in  many  cases  only  by  a  few  fibres.  The  corrosion  of  the  extremity 
of  the  detached  shanks  indicates  that  this  action  had  extended  over  a  considerable 
length  of  tune.  The  unequal  strains  thrown  on  the  rivets  had  been  intensified  by  the 
leverage  of  the  rivet-heads,  and  the  fracture  of  the  fibres,  commencing  at  the  circum- 
ference of  the  shank,  had  taken  place,  as  it  gradually  extended  toward  the  centre,  in 
nearly  every  case  at  the  same  distance  from  the  outer  surface  of  the  conical  head,  so 
that  the  detached  heads  were  concave  at  the  side  where  fracture  had  taken  place.  This 
uniformity  in  the  appearance  of  the  fractures  seems  to  indicate  that  the  iron  of  the  rivets 


418  STEAM  BOILERS.  CHAP.  XVIII. 

was  made  brittle  by  hammering  after  the  rivets  got  cold,  the  injury  extending  to  a 
nearly  uniform  depth  from  the  surface. 

In  locomotive  boilers  the  difference  of  the  temperatures  of  the  flat  sides  of  the  shell 
and  of  the  fire-box,  which  are  tied  rigidly  together  by  closely-spaced  stays,  produces 
often  very  destructive  strains.  Since  the  top  and  side  plates  of  the  fire-box  are  not  at 
liberty  to  expand  freely,  they  pucker  at  the  ends,  causing  the  joints  to  leak  and  often 
fracturing  the  plates  or  the  stay-bolts.  The  tube-sheet  is  likewise  distorted,  the  outer 
rows  of  the  tube-holes  become  oval,  and  the  tube-ends  either  crack  or  leak.  These  evil 
effects  may  be  greatly  lessened  by  turning  the  flanges  with  a  large  radius,  which  allows 
the  plates  to  accommodate  themselves  to  the  varying  movement  of  expansion  and 
contraction.  It  has  also  been  proposed  to  use  flexible  stays  instead  of  screw-stays  near 
the  extremities  of  the  side  and  front  plates  of  the  furnace. 

4.  Formation  of  certain  Saponaceous  Deposits  in  Land  Boilers.— In  an 
article  by  M.  Maurice  Jourdain,  in  the  first  report  of  the  Parisian  Association  of  the 
Owners  of  Steam-apparatus,  an  account  is  given  of  the  formation  of  a  peculiar  deposit 
in  land  boilers  under  certain  conditions.  When  boilers  are  fed  with  water  containing 
greasy  matter  certain  particular  circumstances,  still  imperfectly  defined,  cause  a  light 
grayish,  pulverable  deposit  to  cover  the  iron  directly  exposed  to  the  fire.  This  powder, 
which,  according  to  chemical  analysis,  is  composed  principally  of  lime-salts  and 
magnesia  and  greasy  matter,  possesses  the  peculiar  property  of  being  impervious  to 
water. 

"  It  is  very  easy,"  says  M.  Jourdain,  "to  understand  the  effect  produced  by  this 
lack  of  permeation.  The  water,  running  along  the  plate  without  wetting  it,  is  main- 
tained in  a  spheroidal  state.  Under  these  conditions  the  iron  plate  can  be  highly 
heated  without  communicating  any  sensible  amount  of  heat  to  the  water,  which  covers 
without  touching  it.  This  state  continues  until  the  temperature  of  the  iron  is  suffi- 
ciently high  to  burn  out  the  lime-soap  which  overlays  it.  At  that  moment  the  iron 
plate,  suddenly  uncovered,  is  brought  into  contact  with  the  water,  which  causes  a 
partial  explosion  and  a  sudden  cooling  of  the  metal.  This  suffices  to  deteriorate  the 
boiler. 

"In  fact,  the  deteriorations  observed  in  the  cases  where  that  gray  powder  existed 
have  always  been  very  serious." 

In  1864  six  boilers  erected  in  the  iron-works  of  Mr.  Borsig,  in  Silesia,  showed, 
during  the  first  days  of  use,  leaks  from  the  joints  of  the  iron  plates  exposed  to  the 
fire,  which  daily  increased.  When  the  boilers  were  stopped  a  great  many  cracks  were 
discovered  extending  over  a  large  surface,  besides  loose  rivets,  blisters,  etc.  Three 


SBC.  5.  CAUSES  AND  PREVENTION  OP  THE  DETERIORATION  OP  BOILERS.  419 

• 

other  boilers  put  in  operation  to  replace  the  former  ones  did  not  give  any  better  result. 
After  forty-eight  hours  of  use  the  effect  of  irregular  heating  or  overheating  of  the  iron 
was  indicated  by  the  escape  of  water  and  other  phenomena.  Once,  while  one  of  these 
boilers  was  in  operation,  a  rumbling  noise  was  heard,  followed  by  a  detonation  accom- 
panied by  a  violent  jerking  of  the  boiler,  as  if  it  were  at  the  point  of  exploding.  These 
phenomena  ceased  after  precautions  had  been  taken  to  prevent  the  presence  of  greasy 
matter  in  the  feed-water. 

Several  other  cases  are  described  where  equally  destructive  effects  were  produced  by 
the  formation  of  the  powdery  substance,  which  always  contained  carbonate  of  lime  and 
magnesia  mixed  or  combined  with  greasy  matter. 

In  discussing  these  observations  M.  Delaunay  states  that  he  found  that  the  soap 
formed  by  the  combination  of  carbonate  of  lime  with  fatty  matter  does  not  adhere  to 
the  plates  of  a  boiler,  and  is  permeable  ;  and  he  concludes,  therefore,  that  the  presence 
of  magnesia  may  be  essential  to  give  to  this  substance  the  peculiar  character  which  pro- 
duces such  destructive  effects  on  boilers.  He  continues  then:  "A  final  peculiarity 
which  we  can  select  from  the  detailed  reports  made  on  various  experiments  where  the 
said  phenomena  have  occurred  is  that  the  feed-water  which  caused  them  produced 
always  but  little  incrustation. 

"It  is  comprehensible,  in  fact,  that,  since  the  greasy  matter  contained  in  the  con- 
densed water  is  always  present  in  small  quantities,  its  isolating  action  cannot  become 
manifest  when  it  is  surrounded,  so  to  speak,  by  a  mass  of  chalky  matter,  the  precipi- 
tation of  which  operates  iinceasingly,  adding  at  each  instant  new  layers  of  deposit  to  the 
old  ones.  The  conditions  which  seem  to  determine  the  production  of  the  phenomena  of 
isolation  and  of  the  spheroidal  state,  the  consequences  of  which  we  have  described,  are, 
therefore :  1st,  the  relative  purity  of  the  water ;  2d,  the  presence  of  magnesia  in  the 
water.  Let  us,  however,  remark  that  these  conclusions  are  only  probable,  and  cannot 
be  considered  as  scientifically  demonstrated."  (L.  Delaunay,  '  Etudes  sur  les  Geriera- 
teurs  d  Vapeur  d  Haute  Pression.') 

5.  Corrosion  of  Steam  Boilers  by  Sulphuric  Acid  present  In  the  Soot.— 
Several  years  back  the  attention  of  French  engineers  was  directed  to  the  rapid  corrosion 
of  land  boilers  on  the  exterior  surfaces  of  plates  where  soot  was  allowed  to  accumulate. 
Several  such  cases  are  described  in  an  article  in  the  '  Annales  des  Mines  et  des  Fonts  et 
Chaussees,'  1876. 

In  one  case  the  iron  was  reduced  in  thickness  from  0.47  inch  to  0.067  inch  in  five 
years.  The  corrosion,  which  was  wholly  on  the  outside,  was  attributed  by  Mr.  Dou- 
ville.  Mining  Engineer,  to  the  action  of  the  oxygen  and  sulphurous  acid  in  the  gases  of 


420  STEAM  BOILERS.  CHAP.  XVIII. 

combustion  in  the  presence  of  water.  He  took  large  scales  of  the  oxide  of  iron  from 
the  corroded  parts,  and  he  found  therein  sulphur,  but  was  not  able  to  determine  its 
state  of  combination. 

In  another  similar  case  "  two  specimens  of  the  deposits  left  by  the  smoke  on  the  in- 
jured iron  have  been  analyzed  ;  they  gave  between  52  and  53  per  centum  of  sulphate  of 
iron.  One  gave  1.42  per  centum  of  free  sulphuric  acid,  the  other  gave  12  per  centum 
nearly.  The  deposits  formed  on  the  rest  of  the  boiler  also  contained  sulphuric  acid,  but 
in  notably  less  quantity,  and  no  sensible  deterioration  of  the  metal  had  resulted 
from  it." 

Some  examples  of  exterior  corrosion  in  consequence  of  the  condensation  of  the 
aqueous  vapor  in  the  smoke  on  the  cold  parts  of  boilers  have  been  pointed  out  by  Meu- 
nier-Dollfus,  Director  of  the  Alsatian  Association  of  Steam  Boilers.  Respecting  a  case 
described  by  him  it  is  stated  that  the  corrosion  was  principally  on  the  cold  or  but  little 
warmed  portions  of  the  heaters,  and  had  for  first  cause  the  sulphurous  acid  dissolved  in 
the  water  of  condensation  deposited  from  the  smoke.  It  was  ascertained  that  in  the 
presence  of  air  and  of  this  watery  acid  there  was  first  oxidation  of  the  iron  and  then 
formation  of  the  sulphate  of  the  oxide  of  iron. 

The  following  conclusions  are  drawn  from  the  investigation  of  the  cases  considered  : 
"When  the  smoke-deposits  on  boiler-surfaces  distant  from  the  furnace  are  rendered 
moist  by  any  accidental  cause,  the  sulphurous  acid  in  the  gases  of  combustion  deter- 
mines the  attack  upon  the  metal  by  the  formation  of  the  sulphate  of  the  oxide  of 
iron. 

"  The  attack  can  take  place,  while  the  boiler  is  in  use,  on  such  of  its  metallic  surfaces 
as  may  be  wetted  by  leakage  from  the  boiler  itself,  or  by  water  infiltrated  through,  the 
masonry  or  derived  from  the  condensation  of  the  aqueous  vapor  in  the  gases  of  com- 
bustion by  contact  with  surfaces  relatively  cold.  It  can  also  be  produced,  while  the 
boiler  is  out  of  use,  by  means  of  the  humidity  of  the  air  in  the  flues."  (See  Journal  of 
the  Franklin  Institute,  November,  1877.) 

The  following  is  an  extract  from  an  essay  on  "  The  Acid  Products  of  the  Combustion 
of  Coal,"  by  M.  Vincotte,  translated  in  the  Journal  of  the  Franklin  Institute,  March, 
1880: 

"The  gases  of  combustion  deposit  on  the  heating-surfaces  of  boilers  different  sub- 
stances of  great  importance  as  regards  the  durability  of  the  metal  composing  those  sur- 
faces and  its  power  of  transmitting  heat.  These  substances  are  principally  soot,  tarry 
matter,  sulphuric  acid,  and  ammoniacal  salts. 

"  The  quantity  of  soot  in  the  gases  depends  on  the  kind  of  coal  consumed  and  on 


SEC.  5.  CAUSES  AND  1'REVENTION  OF  THE  DETERIORATION  OP  BOILERS.  421 

tlie  intensity  of  the  chimney-draught ;  but  whether  great  or  small,  a  portion  is  always- 
deposited  on  the  heating-surfaces. 

"  The  soot  in  immediate  contact  with  the  surfaces  is  cooled  by  them  below  the  tem- 
perature of  combustion  ;  but  when  the  deposit  attains  a  certain  thickness  the  portion 
most  distant  from  the  surfaces  burns  whenever  the  hot  gases  of  combustion  passing 
over  it  contain  sufficient  free  oxygen.  The  thickness  of  the  soot-deposit  which  escapes 
combustion  depends  on  the  temperature  of  these  gases  at  any  particular  point  con- 
sidered, and  should,  therefore,  after  the  boiler  has  been  some  time  in  use,  be  found  to 
increase  from  the  furnace  to  the  chimney. 

"  On  all  the  heating-surfaces  where  the  gases  of  combustion  have  a  sufficiently  ele- 
vated temperature  to  burn  the  outer  portion  of  the  soot-deposit-  the  unburnt  inner  por- 
tion is  found  covered  with  a  white  layer  of  ash  from  the  burnt  portion,  and  this  ash 
has  a  thickness  limited  only  by  its  cohesion  ;  generally  it  increases  until  the  surfaces 
are  swept. 

"  On  the  heating-surfaces  where  the  temperature  of  the  gases  of  combustion  is  too 
low  to  ignite  the  soot  the  latter  remains  black,  and  its  thickness  continually  increases 
until  it  falls  off  by  its  own  weight,  which  does  not  happen  soon." 

After  giving  the  analysis  of  several  specimens  of  soot-deposit  taken  from  different 
boilers  and  heaters,  which  contained  in  nearly  every  case  various  quantities  of  ferric 
sulphate,  ferrous  sulphate,  and  free  sulphuric  acid,  he  continues  : 

"  There  does  not  appear  a  satisfactory  theory  of  the  formation  of  the  sulphuric  acid. 
It  may,  indeed,  be  said  that  all  the  coals  burned  in  boilers  contain  sulphur,  whose  com- 
bustion would  naturally  produce  sulphurous  acid,  which  encounters  amid  the  gases  of 
combustion  free  oxygen,  aqueous  vapor,  and  other  substances  necessary  to  its  trans- 
formation into  sulphuric  acid  ;  but  what  those  substances  are  or  how  they  react  is  un- 
known. Be  that  as  it  may  be,  it  is  found  on  all  the  heating-surfaces  not  coated  with 
pitch,  and  forms  there,  in  immediate  contact  with  the  iron  beneath  the  soot,  a  very  thin 
layer  of  ferric  sulphates,  with  which  it  remains  mixed. 

"The  quantity  of  acid  thus  found  on  the  heating-surfaces  is  so  much  the  greater  as 
their  temperature  is  lower.  It  increases  from  the  furnace  to  the  chimney,  and  when 
the  boilers  are  fitted  with  feed-water  heaters  the  acid  is  most  abundant  on  them,  where 
it  is  found  not  only  in  contact  with  the  metal,  but  throughout  the  whole  layer  of  soot 
there,  which  is  impregnated  with  it.  ... 

'  To  sum  up,  when  a  boiler  is  heated  with  semi-fat  coal,  and  examined  after  the  fire 
is  withdrawn,  the  heating-surfaces  are  found  covered  with  the  following  products  of  the 
combustion : 


422  STEAM  BOILERS.  CHAP.  XVIII. 

"1.  Above  the  fire  is  a  thin  layer  of  very  dry  pitch  mixed  with  soot  and  ordinarily  a 
little  acid  and  astringent ;  if,  however,  portions  of  the  surface  have  been  overheated  the 
pitch  will  have  disappeared  from  them.  Upon  the  pitch  is  some  clinker,  derived  from 
the  ash  mechanically  carried  up,  which,  being  intercepted  by  the  rivet-heads  and  other 
projections,  is  partially  fused  there. 

"2.  Farther  on  are  found  three  very  distinct  layers.  The  first,  in  immediate  contact 
with  the  iron,  is  thin  and  white ;  it  is  composed  of  from  80  to  90  per  centum  of  ferrous 
and  ferric  sulphates,  2  to  3  per  centum  of  free  sulphuric  acid,  a  small  quantity  of 
ammoniacal  salts,  sulphate  of  lime,  etc.  Under  this  layer  the  iron  is  white  and  clean  ; 
sometimes  it  is  brilliant. 

"The  next  layer  is  black  soot  mixed  with  a  little  acid,  and  with  salts  of  iron  and 
ferric  oxide,  derived  probably  from  anterior  decompositions.  This  layer  of  black  soot 
increases  in  thickness  as  we  proceed  towards  the  chimney. 

"Lastly,  the  outer  layer  is  composed  of  a  white  or  pinkish  substance,  very  soft, 
very  adhesive,  and  very  dry,  composed  of  alumina,  silica,  and  sulphate  of  lime,  and, 
when  of  great  thickness,  its  external  portion  sometimes  melts  and  forms  small,  greenish, 
vitreous  grains.  Ordinarily  the  layer  is  compact,  but  sometimes  when  very  fat  coal  is 
used  it  is  flaky. 

"3.  Still  farther  towards  the  chimney  the  outer  layer  diminishes  in  thickness  and 
disappears  after  having  become  grayish.  There  is  then  found  only  the  white  and  acid 
substance  in  contact  with  the  iron,  and  the  black  soot,  which  sometimes  becomes  from  f 
to  £  of  an  inch  thick  when  not  removed  by  sweeping. 

"With  fat  coal  the  difference  is  that  the  layer  of  pitch  extends  farther  at  the  ex- 
pense of  the  surface  covered  by  the  acid. 

"As  soon  as  the  boiler  is  put  out  of  use  the  different  products  just  enumerated 
become  rapidly  modified,  and  an  examination  finds  them  under  very  varied  forms. 

"The  sulphuric  acid  quickly  attracts  the  surrounding  humidity,  becomes  diluted, 
and  penetrates  by  imbibition  into  the  soot  which  absorbs  it. 

"The  mixture  of  ferrous  and  ferric  salts  acts  in  an  analogous  way,  depending,  how- 
ever, in  a  very  notable  manner  on  its  composition,  whether  ferrous  or  ferric.  When 
there  is  only  a  little  ferrous  sulphate  it  attracts  enough  humidity  to  furnish  its  water  of 
crystallization,  and  crystallizes  into  a  very  dry  substance,  which  is  only  transformed 
slowly,  and  has  not,  under  ordinary  circumstances,  further  action  on  the  metal.  The 
ferric  salts,  on  the  contrary,  when  in  certain  quantity,  are  deliquescent  or  not,  accord- 
ing to  the  hygrometric  state  of  the  flues.  I  have  had  specimens  which  in  one  corner  of 
my  laboratory  were  deliquescent  and  in  another  warmer  corner  were  not. 


SBC.  6.  CAUSES  AND  PREVENTION  OP  THE  DETERIORATION  OF  BOILEB&  423 

"The  soot,  when  sufficiently  moistened,  diminishes  greatly  in  volume.  It  often  be- 
comes loosened,  twists  like  a  peeling,  and  hangs  from  the  heating-surfaces  in  tatters,  of 
which  a  large  portion  falls  at  the  first  accession  of  heat. 

"The  acid,  once  slightly  diluted,  attacks  the  iron.  The  ferric  salts  act  in  the  same 
manner,  and  after  a  time,  depending  upon  the  humidity  of  the  flues,  the  white  layer  in 
contact  with  the  iron  grows  yellowish,  and  then,  little  by  little,  changes  into  a  thick 
layer  of  rust  impregnated  with  sulphate  of  iron.  It  is  by  the  appearance  of  this  layer, 
after  the  boiler  has  been  some  days  out  of  use,  that  we  ascertain  whether  the  flues  are 
humid.  If  it  grows  yellowish  after  two  or  three  weeks  we  can  conclude  that  the  thick- 
ness of  the  metal  is  rapidly  undergoing  a  general  diminution,  and  this  corrosion  is  due 
to  humidity,  whose  cause  should  be  discovered  and  removed. 

"  As  regards  the  preservation  of  boilers,  all  the  preceding  is  summed  in  some  leading 
facts  : 

"First.  Nearly  all  the  heating-surfaces  of  a  boiler  are  covered  with  sulphuric  acid, 
but  this  acid  attacks  them  only  in  an  insensible  manner.  Boilers  forty  years  old  are 
met  with  whose  heating-surfaces  have  always  been  covered  with  acid  without  diminish- 
ing their  thickness  ^  of  an  inch. 

"Second.  As  soon  as  this  acid  in  any  way  acquires  humidity  it  becomes  very  corro- 
sive and  rapidly  pits  the  iron. 

"  TJiird.  An  examination  of  the  flues  shows  at  a  glance,  simply  by  the  appearance 
of  the  products,  if  humidity  be  present.  If  it  be,  the  cause  must  at  once  be  discovered 
and  the  effects  ascertained.'' 

6.  Corrosion  due  to  the  Presence  of  Oxygen  and  Carbonic  Acid  in 
Water. — The  most  common  cause  of  the  corrosion  of  boilers  is  the  exposure  of  unpro- 
tected iron  surfaces  to  the  combined  action  of  the  atmospheric  air  and  of  water.  The  air 
present  in  the  feed- water  and  the  natural  moisture  of  the  atmosphere  are  sufficient  to 
produce  rusting  /  but  this  action  is  more  intense  when,  after  the  fires  are  hauled,  the 
boilers  are  only  partly  emptied  and  are  left  standing  for  some  time  in  a  damp  condition, 
or  when  leaks  keep  the  outside  of  boilers  wet. 

It  has  been  asserted  by  some  engineers  that  distilled  sea-water  has  a  peculiarly 
destructive  effect  on  iron.  The  corrosive  action  of  such  distilled  water  is,  however,  to 
be  ascribed  to  the  presence  of  some  corrosive  substance  carried  over  during  the  process 
of  distillation,  or  of  atmospheric  air,  oxygen,  or  carbonic  acid ;  because  perfectly  pure 
water  does  not  produce  corrosion  in  iron  at  ordinary  temperatures.  The  carbonic  acid 
may  either  be  originally  present  in  the  free  state  or  may  be  produced  by  the  decompo- 
sition of  some  carbonate. 


STEAM  BOILERS.  CHAP.  XM 11. 

The  following  aocotant  is  given  by  M.  Cornut,  Chief  Engineer  of  the  '"Association  du 
Nord,"  of  experiments  made  by  Scheurer-Kestner  and  Meunier-Bollfus  to  test  the  ac- 
tion of  different  waters  on  iron. 

They  took  three  flasks,  eaeh  holding  ten  litres,  and  tilled  them  with  water. 

The//-.*/  flask  contained  water  free  of  lime-salts  but  highly  aerated. 

The  aftvnd  flask  contained  water  holding  lime-salts  in  solution,  and  likewise  air  and 
carbonic  acid. 

The  M//W  flask  contained  distilled  water  from  which  the  free  oxygen  had  been  re- 
moved by  boiling. 

In  each  flask  a  well-cleaned  and  polished  bar  of  iron  was  placed. 

All  ntHvssjirypiwautionswe.lv  taken  to  ensure  exact  ness  in  these  experiments,  which 
continued  several  weeks. 

Tho.tf/\s7  flask  was  the  first  to  show  signs  of  oxidation.  Yellow  streaks  soon  made 
their  appearance- in  the  water  and  the  bar  became  gradually  covered  with  pustules  of 
rust.  After  all  the  o\\gen  of  the  air  had  been  consumed  the  phenomena  of  oxidation 
ceased  ;  and  the  bar,  having  Ixvn  taken  out  of  the  flask  and  cleaned  Jind  then  put  back. 
remained  as  bright  as  if  it  had  been  varnished. 

The  ,«m>//</  flask  showed  the  same  phenomena  of  oxidation,  but  they  appeared  more 
slowly,  and  the  yellow  streaks  were  intermixed  with  white  streaks  formed  by  lime-salts 
which  were  precipitated.  After  the  lapse  of  some  time  the  iron  bar  was  taken  from  the 
flask,  cleaned  and  put  back,  and  again  Ixrjune  covered  with  a  layer  of  oxide.  Conse- 
quent ly  the  lime-salts  deposited  on  the  metal  interfered  with  and  retarded  its  oxidation. 

The  Mini  flask  showed  no  sign  of  oxidation  ;  the  Ivir  remained  bright. 

Kxperiments  on  the  oxidation  of  iron  by  Professor  K.  rrau-Calvert,  of  Manchester 
v-  Memoirs  of  the  Philosophical  Society  of  Manchester.'  ."nh  vol.,  Tnh  series",  proved  that 
no  oxidation  takes  place  in  iron  immersed  in  dry  oxygen  or  in  pure  and  dry  carbonic 
acid.  Damp  oxygen  acts  feebly,  damp  carbonic  acid  not  at  all.  A  mixture  of  oxygen 
and  carKmie  acid  in  a  dry  state  does  not  oxidi/e  the  iron  :  a  mixture  of  the  two  gases  in 
a  damp  state  produces  a  very  rapid  oxidation  of  the  iron.  First  peroxide  of  iron  is 
formed,  then  carlxwate,  and  finally  a  mixture  of  oxide  and  hydrate  of  the  sesquioxide. 
An  iron  i\xl  plunged  into  a  bottle  filled  with  the  ordinary  water  of  the  city  of  Manches- 
ter, containing  in  solution  oxygen  and  carbonic  acid,  was  covered  with  rust  at  once. 
An  iron  plate,  immersed  in  a  bottle  filled  with  the  same  water  which  had  been  boiled  so 
as  to  remove  the  oxygen  and  carbonic  acid,  showed  no  trace  of  oxidation  after  several 


The  k Third  Report  of  the  Admiralty  Committee  on  Boilers'  contains  the  following 


S«c.  7.  CAUSES  AND  PREVENTION  OP  THE  DETEIIIOHATION  OP  BOILERS.  425 


to  tin-  ilc.strurt  jvi-  action  o|'  water  in  combination  with  oxyir'-n  ari'l  car- 
bonic acid  on  boilers  : 

"  The  water  with  which  the  boilers  are  filled,  and  likewise  that  which  is  supplied  to 
make  up  the  quantity  changed  by  blowing-off  and  the  unavoidable  waste  of  steam,  con- 
tains air  and  carbonic  acid  in  solution  ;  the  air  dissolved  by  water  contains  a  la'rger  pro- 
portion of  oxygen  than  ordinary  atmospheric  air,  and  it  is  this  oxygen  which  contri- 
butes so  greatly  to  the  corrosion  of  iron." 

From  a  series  of  experiments,  carried  out  by  the  committee  to  illustrate  this  action  of 
oxygen  upon  iron  immersed  in  water  under  different  circumstances  at  the  ordinary  tem- 
peratures, it  appears  that  pure  distilled  water  perfectly  free  from  solid  matter  allows  of 
more  corrosion  than  sea-water. 

"  Mr.  Lant  Carpenter  gives  as  the  mean  of  thirty  analyses  the  following  relative  pro- 
portions of  oxygen,  nitrogen,  and  carbonic  acid  in  100  volumes  of  the  gases  dissolved  in 
.surface  sea  -\\-aicr:  Oxygen,  25.1;  nitrogen,  54.2;  carbonic  acid,  20.7;  the  average  pro- 
portion of  these  mixed  gases  amounts  to  2.8  volumes  in  100  volumes  of  water  ;  and  in 
order  to  avoid  the  corrosion  due  to  the  presence  of  these  substances,  and  also  the  varia- 
ble conditions  of  density  and  scale,  the  discontinuance  of  blowing-off,  together  with  the 
substitution  of  distilled  sea-water  (where  fresh  cannot  be  carried)  for  sea-feed  to  make 
up  waste,  would  be  advisable. 

"  Perfectly  dry  air  has  no  action  upon  compact  iron  at  the  ordinary  temperature. 
On  the  other  hand,  water  perfectly  free  from  air  is  also  without  action  upon  iron  at  the 
ordinary  temperature.  Water  in  the  state  of  steam,  when  passed  over  iron  heated  to  a 
sufficiently  high  temperature,  does  oxidize  it.  ... 

"  Much  misapprehension  appears  to  exist  with  reference  to  the  action  of  '•pure  water  ' 
upon  iron,  as,  after  what  has  been  stated,  it  will  be  seen  that  the  corrosion  or  oxidation 
which  has  teen  described  by  many  of  the  witnesses  and  others  to  the  action  of  pure 
waterier  se  should  properly  be  attributed  to  the  oxygen  contained  in  the  air  dissolved 
by  such  water,  the  water  acting  as  a  means  of  transfer  for  the  oxygen  to  the  iron  — 
a  property  which  it  would  possess  to  an  unlimited  extent." 

7.  Corrosive  Action  of  the  Chloride  of  Magnesium.—  The  affinity  of  magne- 
sium for  chlorine  is  so  weak  that  even  at  the  temperature  of  boiling  water  the  chlorine 
decomposes  the  water,  forming  hydrochloric  acid  and  magnesia  according  to  the  fol- 
lowing equation  : 

MgCl,  +  H,O  =  MgO  +  2HC1. 
The  committee  appointed  by  the  British  Admiralty  to  investigate  the  deterioration  of 


426  STEAM  BOILERS.  CHAP.  XVIH. 

boilers  made  experiments  from  which  they  inferred  that  this  decomposition  takes  place 
much  more  slowly  than  has  frequently  been  believed  to  be  the  case. 

"  Some  chloride  of  magnesium  was  dissolved  in  water  and  evaporated  to  dryness  ; 
the  process  was  repeated  (say  20  times)  in  order  to  see  if  the  chloride  would  be  de- 
composed completely.  At  the  end  of  the  experiment  the  residue  (after  heating 
strongly)  was  digested  with  water,  filtered,  and  a  solution  of  nitrate  of  silver  added : 
an  abundant  precipitate  of  chloride  of  silver  showed  that  the  decomposition  was  very 
incomplete. 

"It  was  ascertained  that  so  long  as  the  contents  of  the  dish  were  fluid,  or  even 
after  solidification  commenced,  the  water  evaporated  showed  no  signs  of  acidity,  but 
that,  when  the  last  portions  of  the  water  were  passing  off,  very  marked  acid  reaction 
took  place,  and  the  pungent  vapor  of  hydrochloric  acid  was  distinctly  perceptible. 

"From  these  experiments  it  may  be  inferred  that  no  decomposition  of  chloride  of 
magnesium  occurs  during  the  simple  ebullition  and  concentration  of  sea-water  (as  had 
been  suggested),  and  that  the  water  distilled  from  sea- water,  when  carefully  done, 
contains  nothing  more  than  that  distilled  from  fresh  or  land  water.  When  the  distilla- 
tion is  conducted  on  a  large  scale  and  rapidly,  varying  quantities  of  the  saline  contents 
may  be  carried  over  mechanically  ;  but  the  evil  effects  attributed  to  the  use  of  distilled 
sea- water  are  doubtless  due  to  other  causes. 

"  In  the  presence  of  iron,  as  will  be  shown  further  on,  the  stability  of  chloride  of 
magnesium  is  affected,  with  the  production  of  proto-chloride  of  iron  (ferrous  chloride) ; 
but  the  constant  though  feeble  alkalinity  of  sea-water  precludes  the  action,  or  even 
the  existence,  of  hydrochloric  acid  in  the  free  state. 

"The  instability  of  this  salt  [chloride  of  magnesium]  in  the  presence  of  iron,  even  at 
the  boiling-point  of  water,  and  in  the  absence  of  air,  as  pointed  out  by  Professor  Wag- 
ner (Dingier' s  PolytechniscTies  Journal,  October,  1875),  would  be  considerably  increased 
at  the  higher  temperatures  at  present  realized  in  marine  boilers.  .  .  . 

"In  one  of  the  experimental  tubes  at  Sheerness  (A  No.  21)  there  were  dissolved 
3,000  grains  of  chloride  of  magnesium  in  rain-water  ;  after  six  months'  work  the  rod  in 
the  tube  was  found  to  be  corroded  somewhat  irregularly  from  below  upwards,  which  is 
contrary  to  the  usual  direction.  .  .  . 

"The  water  in  this  tube  was  examined,  and  found  to  contain  proto-chloride  of  iron 
in  solution,  while  at  the  bottom  of  the  tube  there  was  a  deposit  of  red  oxide  of  iron 
which  contained  small  quantities  of  magnesia  ;  now,  proto-chloride  of  iron  and  hydrate 
of  magnesia  react  upon  each  other,  with  the  reproduction  of  chloride  of  mag- 
nesium and  oxide  of  iron,  which  is  gradually  converted  into  the  red  oxide  by  the 


SEC.  8.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OF  BOILERS.  427 

• 

action  of  air ;  the  proportion  of  iron  in  solution  was  equal  to  6.37  grains  in  one  gallon. 
A  continuous  reaction  such  as  this  goes  far  to  explain  why  marine  boilers  raising  steam 
from  sea-water  suffer  so  much  more  from  corrosion  than  boilers  on  shore  fed  with  fresh 
water. 

"Another  source  of  corrosion  connected  with  the  presence  of  chloride  of  mag- 
nesium is  due  to  the  hygroscopic  nature  of  this  salt.  When  chloride  of  magnesium 
is  present  in  the  deposits  formed  in  the  boiler  it  absorbs  moisture  eagerly  from  the 
atmosphere,  and  thus  offers  the  means  of  transferring  oxygen  to  unprotected  iron 
surfaces. 

"  The  phenomenon  known  familiarly  to  engineers  as  sweating  proceeds  from  the  same 
cause,  and  may  always  be  seen  in  the  form  of  globules  on  the  surfaces  of  old  boilers  in 
damp  weather.  These  globules  are  acid  to  test-paper,  and  contain  iron  in  solution  in 
the  state  of  protoxide  ;  on  exposure  to  the  air  they  become  covered  with  a  thin  film  of 
peroxide  of  iron ;  and  if  in  that  condition  the  drops  are  gradually  dried  up  the  film 
(hollow)  remains,  and  if  the  surface  of  the  iron  be  kept  quite  dry  decay  ceases,  but 
recommences  when  the  temperature  of  the  iron  falls  to  that  of  the  atmosphere  and 
allows  of  fresh  moisture  being  deposited."  (Admiralty  Committee  on  Boilers,  Third 
Report.} 

8.  Corrosive  Action  of  Fatty  Acids. — "The  following  is  an  explanation  of  the 
changes  which  a  fatty  body  undergoes  in  presence  of  certain  calcium  and  magnesium 
salts,  especially  the  carbonates.  When  fatty  matters  are  heated  to  a  temperature  of 
about  140°  or  160°  Fahr.  with  calcium  carbonate,  they  form  a  kind  of  insoluble  lime- 
soap,  which  adheres  to  the  sides  of  the  containing  vessel.  As  the  temperature  rises, 
however,  this  lime-soap  is  decomposed  into  free  fatty  acid — Tisually  oleic  acid — and  a 
readily-decomposable  variety  of  basic  lime-soap.  These  two  substances  at  once  seize 
hold  of  the  iron  and  dissolve  it.  The  presence  of  the  grease  is  not  less  destructive  even 
if  the  proportion  of  calcium  and  magnesium  salts  is  very  low,  as,  under  great  pressure, 
a  trilling  amount  of  lime-salts  will  suffice  to  determine  the  re-solution  of  a  neutral  fat 
into  free  acid  and  glycerine."  (G.  ft.  Tweedie,  in  "Iron,"  Sept.  21,  1878.) 

Such  a  decomposition  is,  in  fact,  effected  by  water  alone  when  it  is  made  to  act  upon 
fat  at  high  temperatures  and  pressures,  and  this  process,  called  water-saponification,  has 
been  made  use  of  to  separate  stearic  acid  from  tallow  for  the  purpose  of  manufacturing 
hard  candles.  The  temperature  at  which  this  water- saponification  takes  place  is,  accord- 
ing to  some  authorities,  about  400°  Fahr.,  while  others  assert  that  even  a  temperature 
of  about  270°  Fahr.  would  be  sufficient  for  the  process.  In  several  instances  it  has  been 
found  that  the  iron  boilers  used  in  this  process  of  water-saponification  for  the  manufac- 


428  STEAM  BOILERS.  CHAP.  XVIII. 

% 

ture  of  candles  corroded  rapidly  and  in  a  very  irregular  manner,  the  plates  being  deeply 
pitted,  especially  in  the  neighborhood  of  the  water-level. 

The  corrosive  influence  of  water  and  fatty  acids  upon  iron  at  ordinary  boiler  tempe- 
ratures was  tested  in  1864  by  Professor  A.  W.  Hofmann,  of  the  Royal  College  of 
Chemistry,  by  direct  experiments  which  are  described  by  him  in  a  letter  to  Messrs. 
Humphrys  &  Co.,  appended  to  the  'Eeport  of  the  Admiralty  Committee  on  Boilers.' 
He  says : 

"  Iron  tubes  containing  rods  of  different  varieties  of  iron,  and  fitted  with  hermeti- 
cally-closing caps,  were  charged  with  water  and  stearic  acid,  the  latter  having  been 
separated  from  tallow  by  the  ordinary  process  of  lime-saponification.  These  tubes  were 
exposed  for  three  weeks  to  a  temperature  of  from  264°  to  285°  Fahr.,  corresponding  to  a 
pressure  of  from  2f  to  3£  atmospheres.  On  opening  them  the  inner  surface  of  the  tubes, 
as  well  as  the  iron  rods,  proved  to  be  powerfully  corroded  ;  a  large  proportion  of  oxide 
of  iron  was  found  in  conjunction,  and  apparently  in  combination,  with  the  fatty  acid 
floating  in  the  liquid.  Under  the  circumstances  described  this  eifect  can  have  taken 
place  only  by  an  actual  decomposition  of  water.  Indeed,  when  the  experiment  was 
repeated  with  iron  rods  enclosed  with  water  and  fatty  acids  in  a  glass  tube  the  ends  of 
which  had  been  drawn  out  and  sealed  before  the  blow-pipe,  it  was  found  that  after  six 
hours'  exposure  to  a  temperature  of  356°  Fahr.,  corresponding  to  a  pressure  of  ten 
atmospheres,  very  appreciable  quantities  of  hydrogen  had  been  evolved.  When  the 
drawn-out  point  of  the  tube  was  softened  in  the  blow-pipe  flame  the  compressed  gas 
forced  its  way  through  the  glass  and  exploded  with  -a  loud  sound.  To  ascertain  the 
dependency  of  this  effect,  which  was  observed  in  several  consecutive  experiments,  on  the 
fatty  acid  itself,  and  not  on  traces  of  mineral  acids  possibly  contained  and  masked 
therein,  the  experiment  was  repeated  at  the  reduced  temperature  of  212°  Fahr.,  when 
no  hydrogen  was  found  to  be  evolved.  Had  a  trace  of  free  mineral  acid  been  present 
hydrogen  would  have  inevitably  been  disengaged,  even  at  the  temperature  of  boiling 
water.  It  was,  moreover,  established  by  careful  experiments  that  iron,  when  heated 
with  water  alone  to  356°  Fahr.,  yielded  no  trace  of  hydrogen. 

"  The  rapidity  of  the  corrosive  action  of  fatty  substances,  in  the  presence  of  water, 
upon  iron  considerably  increases  with  the  augmentation  of  temperature,  but  even  at 
ordinary  atmospheric  temperatures  it  takes  place  in  a  lesser  degree." 

The  iron-soap  formed  by  the  action  of  fatty  acids  on  iron  is  decomposed  again  by 
heat  into  oxide  of  iron  and  free  fatty  acid.  A  series  of  observations  and  experiments 
made  on  this  subject  by  Professor  V.  Wartha,  of  Buda-Pesth,  are  recorded  in  Dingier 's 
Polytechnisches  Journal.  Wartha  was  led  to  this  study  by  the  analysis  of  deposits 


SEC.  8.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OF  BOILERS.  429 

found  on  the  damaged  parts  of  the  heater  of  a  steam-engine.  The  analysis  of  that  de- 
posit gave  him  an  oleate  of  the  oxide  of  iron  and  free  oleic  acid. 

"I  made  then  by  synthesis,"  says  Prof.  Wartha,  "a  comparative  trial  with  free 
oleic  acid,  which,  after  having  remained  a  long  time  in  contact  with  the  air,  turned  a 
yellowish  brown.  I  then  took  a  few  cubic  centimetres  of  that  fatty  acid,  added  water 
and  mixed  it  with  iron  filings,  then  heated  it,  when  the  mass  began  to  swell  and  boil 
and  disengaged  great  quantities  of  hydrogen,  and  a  glutinous  mass  of  oleate  of  iron 
remained,  brown  in  color  and  soluble  in  ether.  This  mass  contained  11  per  cent,  of  oxide 
of  iron,  and  was  in  every  respect  like  the  substance  found  in  the  heater. 

"The  explanation  of  the  reactions  which  I  have  just  described  is  very  simple.  In 
the  factory  spoken  of  the  exhaust-steam  is  used  to  heat  the  feed- water.  The  fatty  acid 
— that  is  to  say,  the  oleic  acid— formed  by  contact  with  steam  and  under  the  influence 
of  heat,  is  carried  off  with  the  condensed  steam,  and  arrives  thus  in  the  heater.  In  that 
apparatus  the  drops  of  condensed  oil  stick  to  the  sides  as  a  pasty  mass,  and  under  the 
influence  of  heat  the  iron  is  then  attacked  at  the  point  of  contact. 

"Under  the  influence  of  pressure,  and  with  the  aid  of  hot  water,  oxide  of  iron  and 
free  fatty  acid  are  continually  formed,  and  the  latter  combines  with  a  fresh  portion  of 
iron  to  form  oleate  of  iron ;  so  that  the  drop  eats  away  the  iron,  and  burrows,  so  to 
speak,  in  the  metal.  After  a  very  short  time  the  metal  plates  were  thus  perforated 
and  the  apparatus  commenced  to  leak. 

"By  the  preceding  explanation  it  is  easy  to  account  for  the  manner  in  which  a  com- 
paratively small  quantity  of  oleic  acid  can,  in  a  very  short  time,  perforate  an  iron  plate 
7  millimetres  (0.276  inch)  thick." 

Regarding  the  action  of  fatty  substances  upon  copper  Professor  Hofmann  speaks  as 
follows  in  the  letter  referred  to  above : 

"Under  like  influences  the  behavior  of  metallic  copper  greatly  differs  from  that 
of  iron.  At  ordinary  atmospheric  temperatures  fatty  acids  have  no  action  upon 
copper,  provided  atmospheric  air  be  excluded,  and,  indeed,  even  at  high  temperatures 
metallic  copper  resists  the  action  of  fatty  acids  in  a  remarkable  manner.  The  immense 
copper  condensers  used  at  Messrs.  Price  &  Co.'s  Candle- works  for  condensing  the  pro- 
ducts obtained  by  superheated  steam  saponification  are  week  by  week  exposed  to  the 
simultaneous  action  of  water  and  fatty  acids  at  temperatures  varying  from  520°  to  550° 
Fahr. ;  they  remain  perfectly  intact.  It  is  only  when  the  process  is  interrupted  from 
Saturday  night  till  Monday  morning  that  air  gets  into  the  tubes  and  that  a  slight  corro- 
sion takes  place,  which  is  indicated  by  the  appearance  of  a  bluish  film  on  the  inner  sur- 
face of  the  condenser-tubes.  The  experience  collected  at  Price's  Candle- works,  for 


430  STEAM  BOILERS.  CHAP.  XVIII. 

which  I  am  indebted  to  the  kindness  of  Mr.  Wilson,  entirely  agrees  with  the  results  of 
experiments  which  I  have  made  myself  upon  the  subject.  In  these  experiments  rods  of 
copper  were  enclosed  together  with  water  and  fatty  acids  in  iron  tubes  and  submitted  to 
a  temperature  of  from  264°  to  285°  Fahr.,  corresponding  to  a  pressure  of  from  2J  to  3£ 
atmospheres ;  under  these  conditions  the  copper  rods  were  found  to  be  scarcely  altered. 
Similar  results  were  observed  when  copper  rods  were  heated  with  water  and  fatty  acids 
in  glass  tubes  as  high  as  356°  Fahr. ;  the  fatty  acid  remained  colorless,  and  not  a  trace 
of  hydrogen  was  evolved.  On  the  other  hand,  copper  plates  boiled  with  water  and 
fatty  acids  in  an  open  flask,  provided  with  a  glass  tube  for  the  purpose  of  condensing 
the  steam  and  fat,  were  powerfully  attacked  in  the  course  of  a  few  hours." 

The  water  in  boilers  generally  contains  a  sufficient  quantity  of  lime-salts  to  deter- 
mine the  decomposition  of  fatty  bodies,  and,  when  the  pressure  of  the  steam  exceeds  30 
pounds  per  square  inch  above  the  atmosphere,  its  temperature  is  probably  sufficient  to 
cause  the  decomposition  of  tallow  and  of  the  animal  and  vegetable  oils  used  for  lubri- 
cating the  steam-cylinders  and  valves.  The  conditions  necessary  for  the  decomposition 
of  these  fats  and  the  combination  of  their  acids  with  copper  exist  after  the  engines  are 
stopped  and  atmospheric  air  enters  the  valve-chests,  condensers,  pumps,  and  pipes. 
When  the  engines  are  started  again  the  copper  salts  thus  formed  are  carried  along  with 
the  feed-water  into  the  boilers,  and  as  soon  as  they  are  brought  there  in  contact  with 
metallic  iron  the  fatty  acids  leave  the  copper  and  combine  with  an  equivalent  quantity 
of  iron,  the  metallic  copper  being  deposited  in  the  form  of  minute  particles.  The  quan- 
tity of  iron  primarily  oxidized  in  this  manner  is  relatively  small,  32  parts  of  copper 
combined  with  fatty  acids  being  sufficient  to  oxidize  28  parts  of  iron.  But  the  second- 
ary action  described  by  Professor  Wartha,  and  consisting  in  the  decomposition  of  the 
oleate  of  iron  and  the  recombination  of  the  free  fatty  acid  thus  formed  with  metallic 
iron,  is  a  very  dangerous  source  of  corrosion. 

"The  insolubility  of  the  fatty  acids  in  water  necessitates  their  immediate  contact 
with  the  metallic  iron  surfaces  in  order  that  they  may  effect  corrosion ;  this  contact 
would  be  greatest  at  or  near  the  water-line,  until  the  fat  had  become  so  far  mixed  me- 
chanically with  the  particles  of  solid  matter  in  the  boiler  as  to  give  it  a  greater  specific 
gravity,  when  it  would,  as  it  does  in  practice,  sink  to  the  bottom  of  the  boiler,  where  it 
sometimes  assumes  the  form  of  globular  masses  of  varying  size  produced  by  the  rolling 
motion  of  the  ship."  (See  '  Third  Report  of  the  Admiralty  Committee  on  Boilers?} 

An  instructive  case  of  the  deterioration  of  iron,  apparently  due  to  the  action  of  fatty 
acids,  was  described  by  John  A.  Tobin,  Passed  Assistant  Engineer,  U.S.N.,  in  a  lecture 
delivered  before  the  Massachusetts  Institute  of  Technology. 


SBC.  8.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OF  BOILERS.  431 

The  bottom  sheets  of  the  horizontal  steam-drums  of  the  TJ.  S.  S.  Swatara,  having  a 
thickness  of  f  inch,  were  found  to  be  badly  corroded,  after  two  and  a  half  years'  use,  as 
high  as  the  water  resulting  from  condensation  or  carried  into  the  drums  by  foaming 
had  risen,  and  particularly  along  the  bottom,  which  was  covered  with  a  dark,  greasy 
sludge  mixed  with  a  noticeable  quantity  of  oxide  of  iron.  The  corrosion  of  the  plates 
had  taken  place  in  the  form  of  pitting  and  confluent  honeycombing,  extending  from  the 
merest  impressions  to  a  depth  equal  to  the  thickness  of  the  plates.  Professor  Nichols, 
of  the  Massachusetts  Institute  of  Technology,  analyzed  a  sample  of  the  greasy  deposit, 
and  found  therein  copper  in  combination  with  various  fatty  acids,  such  as  butyric,  oleic, 
stearic,  palmitic  acid,  etc.,  and  he  found  also  particles  of  metallic  copper  present  in  the 
scale  on  the  plate.  After  new  bottoms  were  put  in  the  drums,  and  wrought-iron  steam- 
pipes  connecting  the  drums  with  the  boilers  were  substituted  for  the  copper  ones,  corro- 
sion was  almost  completely  prevented  by  thoroughly  draining  and  cleaning  the  drums 
once  a  month. 

To  prevent  the  action  of  the  fatty  acids  on  condenser-tubes  and  on  steam  and  feed 
pipes  they  are  tinned  when  they  are  made  of  copper  or  brass. 

The  iron  of  the  boilers  may  be  protected  against  the  action  of  the  fatty  acids  by  a 
coating  of  paint  or  cement  or  by  a  thin  layer  of  scale  deposited  on  the  heating-surfaces. 
It  is  necessary  to  form  the  scale  before  the  action  of  the  fatty  acids  on  the  iron  has 
commenced,  because  afterwards  it  is  very  difficult  to  make  the  scale  adhere  to  the  iron, 
although  the  water  may  be  maintained  in  the  boiler  at  a  high  degree  of  saturation. 

It  is  also  proposed  to  neutralize  the  fatty  acids  by  means  of  carbonate  of  soda  or 
caustic  lime,  forming  a  soap.  (See  section  11  of  the  present  chapter.) 

Filters  are  used  to  remove  grease  as  we!1  as  other  foreign  matter  from  the  feed- water 
before  it  enters  the  boiler.  (See  Selderfs  Filter,  section  14,  chapter  xv.) 

Perkins  avoids  entirely  the  use  of  lubricants  in  the  steam-cylinders  and  valves  of  his 
high-pressure  engines  by  employing  a  peculiar  alloy  for  the  wearing-surfaces  of  his 
valves  and  pistons. 

The  formation  of  fatty  acids  is  completely  avoided  by  using  mineral  oils  instead  of 
animal  or  vegetable  oils  or  fats  for  lubricating  the  steam-cylinders  and  valves.  (See 
section  15,  chapter  xvii.) 

To  illustrate  the  difference  in  the  action  of  tallow  or  vegetable  oils  and  of  mineral 
oils  upon  copper,  the  Admiralty  Committee  on  Boilers  placed  coils  of  sheet-brass  in 
common  tallow  and  in  mineral  oil,  and  heated  them  day  by  day  for  four  months,  air 
having  free  access  to  the  surfaces.  "1029.30  grains  of  sheet-brass,  12  inches  long  and  4 
inches  wide,  lost  14.10  grains  in  the  tallow,  which  was  colored  green ;  a  similar  piece  of 


432  STEAM  BOILERS.  CHAP.  XVIII. 

i 

the  same  brass,  weighing  1101.40  grains,  11.90  inches  long  and  4.10  inches  wide,  im- 
mersed in  the  mineral  oil,  lost  0.20  grain,  the  oil  becoming  darker  in  color." 

9.  Corrosion  of  Boilers  by  Galvanic  Action. — When  electro-heterogeneous 
metals  are  brought  in  contact  in  the  presence  of  acids  or  saline  solutions  galvanic  action 
takes  place — that  is  to  say,  the  solution  is  decomposed,  oxygen  being  disengaged  at  the 
electro-positive  pole  of  the  galvanic  couple. 

Copper  has  a  strongly  electro-negative  character  relatively  to  metallic  iron. 

The  contact  of  these  two  metals  in  the  presence  of  water  containing  even  a  minute 
quantity  of  saline  constituents  produces  galvanic  action  ;  the  disengaged  oxygen  of  the 
water  combines  at  once  with  the  iron,  while  the  hydrogen  escapes  at  the  pole  formed  by 
the  copper,  leaving  the  latter  unaltered.  In  this  manner  a  minute  quantity  of  copper 
may  cause  the  oxidation  or  corrosion  of  a  large  quantity  of  iron,  if  metallic  contact  is 
maintained  between  the  two  metals. 

On  account  of  this  action  the  use  of  copper  tubes  in  marine  boilers  is  inadmissible. 
Copper  is  frequently  carried  into  the  boiler  by  the  feed-water  ;  minute  particles  may  be 
abraded  from  the  copper  and  composition  pipes  by  the  steam  and  water  flowing  through 
them  ;  and  the  salts  formed  by  the  combination  of  copper  with  fatty  acids  are  decom- 
posed when  they  come  in  contact  with  the  iron  of  the  boiler,  and  metallic  copper  is  de- 
posited. (See  section  8  of  tlie present  chapter.') 

Particles  of  metallic  copper  have  frequently  been  found  on  pitted  and  honeycombed 
boiler-plates,  and  this  peculiar  form  of  corrosion  has  been  ascribed  to  the  continued 
galvanic  action  of  these  detached  particles.  It  is,  however,  difficult  to  decide  how 
much  of  the  corrosion  was  due  to  the  action  of  fatty  acids  and  how  much  of  it  was 
caused  by  the  galvanic  action  of  the  copper.  The  Admiralty  Committee  on  the  Deterio- 
ration of  Boilers  was  inclined  to  ascribe  but  a  small  share  of  the  corrosion  of  boilers  to 
the  latter  cause,  because  the  conditions  which  usually  prevail  in  marine  boilers  prevent 
immediate  contact  between  the  small  particles  of  copper  and  the  clean  metallic  surfaces 
of  the  iron  plates. 

Lead  is  likewise  an  electro-negative  metal  relatively  to  iron.  The  corrosion  of  the 
plates  in  the  vicinity  of  manholes  and  mudholes  is  ascribed  to  galvanic  action  caused 
by  the  presence  of  lead,  derived  from  the  white  and  red  lead  used  in  making  the 
joints. 

In  order  to  prevent  galvanic  action  it  has  been  recommended  to  obtain  electro-homo- 
geneity in  the  boiler  by  using  only  one  kind  of  iron,  and  iron  tubes  instead  of  brass  tubes, 
and,  when  steel  is  used,  to  employ  it  for  every  part  of  the  boiler  and  not  in  combina- 
tion with  iron.  It  is,  however,  impracticable  to  get  large  quantities  of  iron  or  steel  of  a 


SEC.  9.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OF  BOILERS.  433 

perfectly  uniform  character,  which  would  be  necessary  in  order  to  ensure  perfect  elec- 
tro-homogeneity. 

There  is  also  no  direct  evidence  that  brass  tubes  hasten  the  corrosion  of  boilers  ;  on 
the  contrary,  the  inner  surface  of  iron  tube-plates  with  brass  tubes  appears  generally 
to  be  little  attacked  by  corrosion. 

The  introduction  of  copper  into  boilers  is  prevented  by  tinning  copper  and  composi- 
tion steam-pipes,  feed-pipes,  and  condenser-tubes,  by  using  mineral  oils  as  lubricants 
for  the  steam-cylinders  and  valves,  and  by  filtering  the  feed- water. 

Galvanic  action  may  be  effectually  prevented  by  keeping  the  surfaces  of  the  boilers 
covered  with  a  coating  of  firm  scale  or  paint. 

Feldbacher's  plan  of  lining  the  interior  of  the  boiler  with  sheet-copper  has  been 
tried  on  land  boilers,  and,  it  is  claimed,  with  good  results,  corrosion  being  prevented 
and  incrustation  greatly  lessened.  Another  patentee  coats  the  interior  of  the  boiler 
with  a  mere  film  of  copper  deposited  from  a  solution  of  cyanide  of  copper.  Other 
patents  have  been  secured  for  coating  the  interior  surfaces  of  boilers  with  tin,  also  for 
enamelling  and  electro-coppering  iron  tubes.  But  none  of  these  plans  have  come  into 
extensive  use  in  marine  boilers. 

The  film  of  black  magnetic  oxide  of  iron  which  covers  a  boiler-plate  when  it  leaves 
the  rolls  in  a  finished  state  affords  to  the  iron  complete  protection  against  corrosion  as 
long  as  it  adheres  firmly  and  remains  unbroken.  When  this  film  is  thick  it  is  easily  de- 
tached from  the  plate,  and  its  thickness  depends  upon  the  temperature  of  the  iron  at  the 
time  of  rolling.  Much  of  this  film  is  detached  by  the  rough  usage  to  which  the  plates 
are  subjected  in  transportation  and  in  the  boiler-shop,  and  by  the  various  processes  of 
boilermaking. 

Professor  Barff  produces  a  firmly-adhering  coating  of  this  black  oxide  artificially 
by  heating  articles  of  cast  or  wrought-iron,  the  surfaces  of  which  have  been  carefully 
cleaned,  to  a  high  temperature  in  a  closed  chamber  from  which  the  atmospheric  air 
has  been  removed,  and  subjecting  them  to  the  action  of  superheated  steam.  He 
states  that  the  temperature  required  for  this  process  ranges  from  650°  to  1,500°  Fahr.  ; 
the  lower  temperature  and  longer  treatment  for  wrought-iron,  the  more  rapid  treatment 
and  higher  temperature  for  cast-iron.  The  application  of  this  process  to  finished  boilers 
has  been  suggested,  but  has  not  been  practically  tested. 

A  film  of  this  black  oxide  protects  iron  against  the  attack  of  powerful  acids.  From 
experiments  made  by  Schonbein  and  others  it  appears  that  this  oxide  of  iron  has  an 
electro-negative  character  far  greater  than  copper  and  nearly  equal  to  that  of  platinum. 
This  fact  may  explain  the  rapid  corrosion  of  iron  at  places  where  this  film  has  been 


434  STEAM  BOILERS.  CHAP.  XVIII. 

broken,  since  a  powerful  galvanic  action  might  be  produced  under  favorable  circum- 
stances by  the  contact  of  this  oxide  and  of  the  pure  iron,  the  former  forming  the  nega- 
tive and  the  latter  the  positive  pole  of  a  galvanic  battery.  On  this  account  some  manu- 
facturers of  boilers  remove  carefully  the  whole  film  of  oxide  from  boiler-plates,  since  it 
cannot  be  maintained  unbroken  in  a  boiler  and  would  rather  hasten  than  prevent  its 
corrosion. 

The  corrosive  effect  of  galvanic  action  on  iron  boilers  may  be  prevented  by  rendering 
them  the  negative  pole  of  an  electric  battery.  This  is  generally  and  most  successfully 
accomplished  by  placing  within  the  boiler  and  connecting  with  the  shell  a  metal  which 
has  a  stronger  electro-positive  character  than  iron.  The  metal  generally  used  for  this 
purpose  is  zinc. 

1O.  The  Use  of  Zinc  for  the  Prevention  of  Corrosion  and  Incrustation 
of  Boilers. — Very  conflicting  accounts  are  given  by  engineers  about  the  efficacy  of  zinc 
in  preventing  the  corrosion  of  boilers.  From  the  varied  testimony  offered  on  this 
point,  and  from  the  results  of  a  series  of  experiments,  the  Admiralty  Committee  on 
Boilers  drew  the  following  conclusions,  which  are  given  in  their  'Third  Report '- 
viz.  : 

"Apart  from  any  consideration  as  to  the  existence  of  galvanic  action  in  boilers,  the 
protective  value  of  zinc  may  be  stated  as  follows  :  If  a  boiler  is  worked  in  the  ordinary 
manner  with  sea- water  its  exposed  surfaces  will  be  vulnerable  to  the  action  of  all  the 
corrosive  influences  which  may  be  present  capable  of  affecting  iron  ;  but  if  zinc  be  in- 
troduced and  applied  in  the  manner  which  has  already  been  pointed  out — i.e.,  perfect 
metallic  continuity  ensured  between  it  and  the  iron — galvanic  action  is  set  up  between 
the  two  metals,  and  the  latter  is  compelled,  by  the  presence  of  one  of  a  more  electro- 
positive nature,  to  assume  a  negative  condition  towards  corrosion  or  oxidation. 

"  Such  being  the  case,  the  metallic  condition  of  the  iron  is  preserved  at  the  expense 
of  the  zinc,  which  loses  in  course  of  time  its  metallic  nature  by  oxidation,  in  which 
latter  condition  it  ceases  to  afford  protection  and  must  therefore  be  renewed  at  intervals. 
In  cases  where  this  metallic  contimiity  has  not  been  effected  the  zinc  would  share  with 
the  iron  surfaces  of  the  boiler  any  corrosive  action  that  might  be  present,  in  proportion 
to  the  surface  exposed,  which,  in  any  case,  would  be  relatively  small.  There  would  be 
no  electro-chemical  relation  between  the  metals,  and  the  different  results  observed  by 
marine  engineers  may  have  depended  upon  the  fortuitous  circumstance  that  in  some 
cases  metallic  continuity  has  been  unintentionally  effected  in  suspending  the  zinc  from 
the  stays  of  the  boiler  ;  this  seems  to  be  a  very  probable  explanation  of  the  discordant 
opinions  held  by  many  as  to  the  protective  value  of  zinc," 


SEC.  10.  CAUSES  AND  PREVENTION  OF  THE  DETERIORATION  OF  BOILERS.  435 

Zinc  has  also  been  found  to  prevent  the  formation  of  adhesive  scale  in  land  boilers 
fed  with  calcareous  water.  The  mode  of  action  of  zinc  in  this  respect  is  described  by 
Brossard  de  Corbigny,  in  an  article  in  the  Annales  des  Mines  of  1877,  which  has  been 
translated  for  the  Journal  of  the  Franklin  Institute  of  January,  1878,  and  from  which 
the  following  is  extracted : 

"  When  the  water  is  but  little  calcareous  the  deposits,  instead  of  forming  solid  and 
adherent  scale,  remain  in  the  state  of  fluid  mud,  easily  removable  by  simple  washing. 
The  iron  being  clean  and  not  rusted,  no  picking  or  scraping  is  needed,  which  effects  a 
great  economy  of  time,  hard  labor,  and  oversight. 

"  When,  however,  the  water  is  strongly  calcareous  the  deposits  are  as  coherent  and 
stony  as  though  the  zinc  had  not  been  employed ;  but,  what  is  extremely  important,  this 
scale,  while  acquiring  its  thickness  and  hardness,  does  not  adhere  to  the  iron.  It  can 
be  pulled  off  by  hand,  or,  at  worst,  detached  without  much  effort,  leaving  the  iron 
clean.  A  simple  washing  removes  it  from  the  boiler,  and  in  this  case,  as  in  the  previ- 
ous, picking  and  scraping  are  avoided." 

The  following  hypothesis  is  advanced  to  explain  this  action : 

"  The  two  metals,  iron  and  zinc,  surrounded  by  water  at  a  high  temperature,  form  a 
voltaic  pile  with  a  single  liquid,  which  slowly  decomposes  the  water.  The  liberated 
oxygen  combines  with  the  most  oxidizable  metal — the  zinc — and  its  hydrogen  equivalent 
is  disengaged  at  the  surface  of  the  iron.  There  is  thus  generated,  over  the  whole  ex- 
tent of  the  iron  influenced,  a  very  feeble  but  continuous  current  of  hydrogen,  and  the 
bubbles  of  this  gas  isolate  at  each  instant  the  metallic  surface  from  the  scale-forming 
substance.  If  there  is  but  little  of  the  latter  it  is  penetrated  by  these  bubbles  and  re- 
duced to  mud ;  if  there  is  more,  coherent  scale  is  produced,  which,  being  kept  off  by 
the  intervening  stratum  of  hydrogen,  takes  the  form  of  the  iron  surface  without  adher- 
ing to  it. 

"Zinc  introduced  into  a  boiler  whose  surfaces  had  been  imperfectly  freed  of  scale 
has  the  property  of  detaching  the  remainder.  This  effect  is  well  explained  by  the  action 
of  a  feeble  disengagement  of  gas  beneath  the  scale,  raising  it  little  by  little  and  separat- 
ing it  from  the  iron." 

With  the  selenious  water  of  the  slate-works  of  Angers  the  addition  of  zinc  gave  no 
useful  result ;  the  scale  adhered  strongly  to  the  iron ;  but  the  writer  does  not  venture  to 
say  whether  this  result  was  to  be  attributed  to  the  more  coherent  nature  of  pure  sul- 
phate of  lime,  of  which  the  scale  almost  entirely  consisted,  or  to  an  insufficient  quantity 
of  zinc  employed. 

The  action  of  zinc  with  sea- water  and  acid  water  was  not  investigated  by  the  writer. 


436 


STEAM  BOILERS. 


CHAP.  XVIII. 


Fig.147a. 


With  water  containing  free  acid,  however,  no  good  results  would  be  obtained,  as  the 
zinc  would  be  corroded  very  rapidly  and  too  large  a  quantity  would  be  required. 

De  Corbigny  recommends  that  in  boilers  fed  with  fresh  water  from  half  a  pound  to 
one  and  a  half  pounds  of  zinc  should  be  used  for  each  five  square  feet  of  water-heating 
surface  during  several  months,  and  that  the  zinc  should  be  used  in  the  form  of  pigs  or 
cubical  masses,  and  not  in  the  form  of  chippings  or  sheets,  since  in  the  latter  case  the 
electro-chemical  action,  being  exerted  over  too  large  a  surface,  becomes  too  rapidly 
exhausted. 

Other  writers  recommend  20  inches  of  area  for  each  horse-power,  and  for  marine 
boilers  at  least  a  quarter  of  a  pound  for  each  square  foot  of  grate-surface. 

The  zinc  slabs  should  be  distributed  over  different  parts  within  the  water-space  of 
the  boiler ;  but  they  should  not  be  suspended  directly  over  the  furnaces  or  back-connec- 
tions, where  the  oxide  of  zinc,  as  it  drops  down,  may  cause  blistering  and  burning. 
When  zinc  is  placed  in  steam  drums  and  pipes  the  oxide  is  sometimes  carried  by  the 
steam-currents  into  the  valves  and  causes  injury  to  them. 

Figure  147a  shows  an  arrange- 
ment adopted  in  some  boilers  for 
]  securing  the  zinc.  Zinc  slabs  about 
15"  X  12"  X  1"  are  bolted  to  iron 
clamps  and  secured  by  them  firmly 
to  the  iron  stay-rods  or  tubes.  It  is 
important  that,  so  far  as  it  is  practi- 
cable, no  water  should  get  between 
the  zinc  and  the  iron.  To  ensure 
perfect  metallic  continuity  between 
the  two  metals  the  zinc  is  some- 
times soldered  to  the  iron  or  zinc  studs  are  screwed  into  the  shell  of  the  boiler. 

The  '  Steam  Manual,'  issued  by  the  English  Admiralty  (1879),  contains  the  following 
instructions  regarding  the  use  of  zinc  in  boilers  :  "  The  zinc  slabs  appear  to  deteriorate 
either  by  gradually  wasting  away  or  by  gradual  change  of  substance.  In  this  latter 
case,  which  is  the  most  common,  the  zinc  slab  gradually  becomes  black  in  color,  brittle, 
and  friable  ;  and  when  it  has  been  long  exposed  the  mere  pressure  of  the  hand  is  suffi- 
cient to  reduce  it  to  powder.  Experience  alone  will  enable  the  engineer  officer  to  deter- 
mine how  far  the  zinc  may  be  allowed  to  decay  before  renewal ;  but,  until,  that  experi- 
ence is  gained,  it  is  recommended  that  the  zinc  should  be  renewed  as  soon  as  the  decay 
has  penetrated  a  quarter  of  an  inch  below  the  surface.  Under  ordinary  conditions  of 


SEC.  11.  CAUSES  AND  PREVENTION  OP  THE  DETERIORATION  OP*  BOILERS. 

working  the  zinc  slab  may  be  expected  to  last,  when  the  boilers  are  new  and  the  zinc 
good,  not  less  than  from  two  to  four  months  under  water. 

"  Good  zinc  is  to  be  used  for  these  slabs.  Zinc  '  bottoms '  must  not  be  used,  and  the 
remains  of  slabs  which  have  been  in  use  must  not  be  recast  on  board  ship  for  further 
use.  If  upon  examination  they  are  not  sufficiently  decayed  to  be  rejected  altogether 
the  decayed  parts  may  be  chipped  off  and  the  slab  refitted  and  kept  in  use  for  some 
time  longer.  When  the  slabs  are  finally  removed  from  the  boilers  they  are  to  be  broken 
up,  the  decayed  portions  thrown  aside  as  useless,  and  such  of  the  remains  as  appear  to 
consist  of  good  zinc  preserved  and  returned  into  store." 

11.  Action  of  various  Substances  upon  the  Incrustative  and  Corrosive 
Ingredients  of  Feed-waters. — The  substances  used  to  prevent  the  formation  of  hard, 
adhesive  scale  and  the  internal  corrosion  of  boilers  are  either  introduced  directly  into 
the  boiler,  or  they  are  mixed  with  the  feed- water  and  made  to  act  upon  the  salts  and 
acids  contained  in  the  water  before  it  enters  the  boiler.  When  the  latter  method  is  used 
tanks  of  large  capacity  have  generally  to  be  provided  in  order  to  allow  time  for  the 
completion  of  the  process  of  purification.  On  board  of  vessels  there  is  generally  no 
room  for  such  tanks,  and  the  action  of  neutralizing  the  incrustative  and  corrosive  pro- 
perties of  the  feed- water  has  to  take  place,  in  part  at  least,  within  the  boiler. 

.  Many  of  the  substances  recommended  for  the  prevention  of  incrustation  act  by  a 
mechanical  process,  while  others  effect  a  chemical  reaction,  either  changing  the  carbon- 
ates and  sulphates  of  lime  into  soluble  salts  of  lime  or  producing  insoluble  salts  of  lime 
and  magnesia,  which  are  either  precipitated  as  an  incoherent  mass  or  remain  suspended 
in  the  water  without  agglutinating. 

The  anti-corrosive  remedies  are  intended  especially  to  change  the  chloride  of  magne- 
sium and  the  fatty  acids  into  substances  which  do  not  corrode  the  metal  of  the  boiler, 
are  not  readily  redecomposed  under  the  conditions  obtaining  in  a  steam  boiler,  and 
either  pass  off  with  the  steam  in  the  form  of  gas  or  can  be  removed  from  the  boiler  by 
the  ordinary  process  of  blowing-off. 

The  selection  of  any  of  these  remedies  should  always  be  preceded  by  a  careful  ana- 
lysis of  the  water  used  for  feeding  the  boiler.  The  presence  of  certain  substances  may 
not  only  neutralize  the  effect  of  a  chemical  agent,  but  cause  reactions  which  produce 
even  more  harmful  substances.  In  several  instances  remedies  have  been  proposed  which 
increased  corrosion  while  they  prevented  incrustation,  and  others  produce  practical  dif- 
ficulties which  render  their  use  not  only  inconvenient  but  dangerous. 

The  chemical  treatment  of  the  water  of  marine  boilers  is  more  difficult  than  that  of 
the  water  of  most  land  boilers,  on  account  of  the  greater  number  of  ingredients  con- 


438  STEAM  BOILERS.  CHAP.  XVIII. 

tained  in  the  former,  and  because  the  method  of  purification  in  tanks  is  not  admissible 
on  board  of  vessels. 

"The  present  large  capacity  of  marine  boilers  using  sea- water  alone  renders  any 
complete  chemical  treatment  of  the  water,  with  the  object  of  preventing  corrosion,  ex- 
tremely difficult,  as,  besides  sulphate  of  lime,  sea-water  contains  salts  of  magnesium, 
which,  in  any  attempt  towards  a  condition  of  alkalinity  by  lime  or  carbonate  of  soda, 
must  be  decomposed  with  production  of  a  bulky  precipitate  of  magnesia ;  and  this, 
added  to  the  sulphate  of  lime,  may  induce  priming,  and  would  increase  the  difficulties 
resulting  from  the  accumulation  of  solid  matter  on  the  evaporating  surfaces,  unless  the 
quantity  of  scale  be  limited  by  substituting  distilled  sea-water  for  the  feed  from  the  sea 
itself."  (See  '  TJiird  Report  of  the  Admiralty  Committee  on  Boilers.') 

The  many  anti-corrosive  and  anti-incrustative  remedies  offered  for  sale  contain,  in 
some  form  or  other,  one  or  several  of  the  following  ingredients  combined  in  a  more  or 
less  judicious  manner : 

Oil-cakes,  potatoes,  and  other  starchy  matter  are  sometimes  put  into  the  boiler  to 
prevent  the  formation  of  hard  scale  by  enveloping  the  particles  of  lime  so  that  they  are 
deposited  in  the  form  of  mud ;  but  they  produce  frothing,  and  often  cause  the  boiler  to 
foam  badly. 

Glue,  offal  of  hoofs  and  horns,  tobacco-juice,  Irish  moss,  peat,  tow,  hemp,  etc.,  act 
in  a  similar  manner. 

Clay  likewise  causes  the  lime-salts  to  settle  down  as  a  soft  mud ;  but  a  grave  objec- 
tion to  its  use  are  the  gritty  particles  of  sand  contained  in  it,  which,  earned  over  by  the 
steam,  injure  the  valve-faces. 

Various  varnishes  or  lacquers  are  proposed  to  prevent  incrustation,  but  the  pre- 
sence of  fatty  matter  in  them  often  increases  corrosion,  and  they  afford  insufficient  pro- 
tection against  incrustation. 

The  action  of  petroleum  or  paraffine-oil  as  a  protection  from  incrustation  is  involved 
in  obscurity,  but  its  effects  are  reported  on  favorably.  It  is  said  to  penetrate  and  rot 
the  scale,  making  it  porous  and  easily  removed,  the  quantity  used  being  about  one 
quart  per  week  for  a  twenty-five  horse-power  boiler.  The  most  efficient  qiiality  is  the 
heavy,  unrefined  oil,  the  other  being  soon  expelled  by  the  heat.  The  oil  may  also  be  ap- 
plied to  the  iron  as  a  coating.  (See  section  14,  chapter  xvii.) 

Glycerine  has  been  used  in  Europe  in  steel  boilers  to  prevent  the  adhesion  of  scale. 

Milk  of  lime  or  hydrate  of  lime  added  to  water  takes  up  the  excess  of  carbonic  acid, 
which  enables  the  water  to  hold  the  carbonate  of  lime  in  solution,  and  the  latter  is  thus 
precipitated.  This  process,  known  as  Clark's,  recommends  itself  through  its  cheapness 


SKC.  11.  CAUSES  AND  PREVENTION  OP  THE  DETERIORATION  OF  BOILERS.  439 

and  simplicity  where  tanks  can  be  provided  for  carrying  it  on.     It  is  used  to  purify  the 
water  of  locomotive  and  stationary  boilers. 

A  solution  of  caustic  lime  being  added  to  sea- water  has  the  effect  of  decomposing  the 
chloride  of  magnesium  and  sulphate  of  magnesia,  with  the  formation  of  the  correspond- 
ing salts  of  lime,  magnesia  being  liberated. 

Hetet  (Pharmacien-en-chef  de  la  Marine)  has  made  extensive  experiments  at  Brest 
with  a  process  of  neutralizing  the  fatty  acids  contained  in  the  condenser-feed  by  means 
of  lime-water.  The  quantity  of  lime  used  by  him  is  equal  to  about  one-tenth  of  the 
weight  of  oil  used  as  a  lubricant  in  the  cylinders  of  the  engines.  The  lime  forms  with 
the  grease  an  insoluble  soap,  which  is  found  in  the  bottom  of  the  boilers  or  of  the  puri- 
fying-tank. This  process  should  always  be  carried  on  in  tanks,  and  the  water  should 
be  filtered,  so  that  the  lime-soap  does  not  enter  the  boiler,  where,  under  the  influence  of 
heat  and  in  contact  with  the  iron,  it  would  probably  be  decomposed.  (See  section  8 
of  the  present  chapter.} 

Carbonate  of  soda,  caustic  soda,  and.  potash  cause  the  carbonates  of  lime  and  mag- 
nesia to  be  precipitated  by  combining  with  the  free  carbonic  acid,  forming  soluble  car- 
bonates or  bicarbonates  of  soda  and  potash. 

Carbonate  of  soda  decomposes  the  sulphate  of  lime,  forming  sulphate  of  soda,  which 
is  held  in  solution,  and  carbonate  of  lime,  which  is  precipitated. 

By  combining  with  the  free  carbonic  acid  in  the  feed- water  these  alkalies  remove  a 
very  harmful  corrosive  element.  (See  section  6  of  the  present  chapter.)  They  also  effec- 
tually neutralize  the  fatty  acids  by  forming  a  soluble  soap  which  is  not  readily  decom- 
posed. 

The  '  Admiralty  Instructions '  relating  to  the  machinery  of  English  naval  vessels  pro- 
vide that,  with  a  view  to  determine  the  condition  of  the  water  in  the  boilers  as  regards 
its  acidity,  neutrality,  or  alkalinity,  the  water  of  each  boiler  is  to  be  tested  with  test- 
paper  at  least  once  per  day  when  under  steam.  Should  the  water  in  the  boilers  be 
found  to  be  in  an  acid  condition  a  small  quantity  of  carbonate  of  soda  is  to  be  sup- 
plied to  the  boiler  to  neutralize  the  acid  in  the  water.  The  soda  should  be  put  into 
the  condenser  or  hot- well,  from  which  it  will  be  pumped  into  the  boilers  with  the  feed- 
water. 

It  is  recommended  to  use  carbonate  of  soda  in  connection  with  lime  or  other  in- 
gredients for  the  prevention  of  scale  and  corrosion.  First,  by  adding  a  solution  of 
caustic  lime  to  the  feed- water,  the  chloride  of  magnesium  and  sulphate  of  magnesia  are 
to  be  decomposed,  with  formation  of  the  corresponding  salts  of  lime,  magnesia  being 
liberated ;  then  carbonate  of  soda  is  to  be  supplied,  which  will  decompose  those  two 


440  STEAM  BOILERS.  CHAP.  xvm. 

lime-salts,  forming  carbonate  of  lime,  which,  is  precipitated,  and  chloride  of  sodium  and 
sulphate  of  soda,  which  remain  in  solution. 

"The  use  of  carbonate  of  soda  in  limited  quantity,  with  the  idea  that  it  neutralizes 
the  effect  of  fatty  acids  in  marine  boilers  raising  steam  from  sea- water,  is  questionable, 
because  so  long  as  chloride  or  sulphate  of  magnesia  remains  in  the  water  the  carbonate  of 
soda  is  immediately  decomposed  with  the  result  as  stated  above.  It  is  only  when  those 
two  salts  have  been  wholly  decomposed,  and  the  sulphate  of  lime  in  solution  has  been 
converted  into  carbonate,  that  the  carbonate  of  soda  can  be  potential  as  such.  So  far  as 
the  committee  are  aware  this  condition  has  never  been  realized  in  marine  boilers,  and  it 
is  for  this  reason  that  the  benefit  which  would  have  resulted  from  the  use  of  a  limited 
quantity  of  soda  (in  fresh  water)  has  not  existed.  .  .  . 

"  The  quantity  of  soda  required  for  the  complete  decomposition  of  the  magnesium 
and  calcium  salts  is  easily  ascertained.  To  replace  magnesium  in  any  of  its  compounds 
by  sodium  it  is  necessary  to  make  use  of  23  parts  of  the  latter  for  12  parts  of  the 
former,  and  similarly  to  replace  the  calcium  (the  equivalent  of  which  is  20)  also  requires 
23  parts  ;  or,  taking  the  oxides  of  these  metals,  lime,  magnesia,  and  soda,  their  respec- 
tive equivalent  values  are  28,  20,  and  31.  There  are  in  a  ton  of  ordinary  sea- water 
19,837  grains  of  magnesium  and  7,233  grains  of  calcium,  and  to  replace  these  two  by 
sodium  there  are  required  46,339  grains  of  that  metal.  The  weight  of  crystallized  car- 
bonate of  soda  which  contains  23  parts  or  one  equivalent  of  sodium  is  143,  so  that 
46,339  x  143  -f-  23  =  288,107  grains,  or  41  pounds,  2  ounces,  232  grains,  are  the  quantity 
of  crystals  of  carbonate  of  soda  required  for  one  ton  of  sea- water."  (Report  of  Admi- 
ralty Committee  on  Boilers.} 

Hyposulphite  of  soda  keeps  the  salts  of  lime  in  solution ;  oxalate  of  soda  causes  their 
precipitation  as  a  loose  deposit ;  but  both  are  expensive. 

Proto-chloride  of  tin,  silicate,  phosphate,  and  arseniate  of  soda  have  been  tried, 
but  are  too  expensive,  and  are  not  found  to  answer  their  purpose  sufficiently 
well. 

Chloride  of  ammonium,  or  sal-ammoniac,  acts  on  the  carbonate  of  lime  and  magne- 
sia, converting  them  into  chlorides,  while  their  carbonic  acid  goes  to  the  ammonium, 
forming  carbonate  of  ammonia,  which  escapes  with  the  steam.  Sulphate  of  lime  is  not 
affected  by  sal-ammoniac. 

Tannic  acid  forms  insoluble  tannates  of  lime  and  magnesia  by  the  decomposition 
of  the  carbonates.  These  tannates  have  a  low  specific  gravity  and  float  about  the  water 
instead  of  agglutinating  into  a  crust.  The  sulphates  and  chlorides  are  not  acted  upon 
by  tannic  acid,  and  will  incrustate  notwithstanding  its  presence.  Free  tannic  acid  at- 


SEC.  11.  CAUSES  AND  PREVENTION  OP  THE  DETERIORATION  OF  BOILERS.  441 

tacks  the  iron,  and  its  presence  in  a  boiler  is  a  source  of  great  danger.  Its  effect  may  be 
neutralized  by  carbonate  of  soda. 

Tannin-bearing  bodies,  like  oak  and  hemlock  bark,  logwood,  catechu,  leather,  or  ex- 
tracts made  of  them,  are  frequently  introduced  into  boilers  for  the  prevention  of  scale. 
When  the  solid  bodies  are  used  there  is  danger  of  pieces  of  bark,  etc.,  being  blown  over 
by  the  steam  into  the  valves  and  pipes. 

Tannate  of  soda,  being  introduced  into  a  boiler  where  the  carbonates  of  lime  and 
magnesia  are  present,  gives  up  to  them  its  tannic  acid  to  form  the  insoluble  tannates, 
and  takes  up  their  carbonic  acid  to  form  carbonate  of  soda,  which  in  turn  reacts  on  the 
sulphate  of  lime,  converting  it  into  carbonate  of  lime  and  bringing  it  thus  under  the 
inihience  of  a  fresh  portion  of  tannate  of  soda.  The  constant  presence  of  the  soda  pro- 
tects the  iron  from  the  corrosive  action  of  tannic  acid  as  well  as  of  carbonic  acid.  The 
same  reaction  takes  place  between  tannate  of  soda  and  the  already  existing  scale,  but 
more  slowly  than  when  the  salts  are  held  in  solution. 

Acetic  acid  converts  the  carbonates  into  soluble  acetates ;  but  the  iron  is  equally  ex- 
posed to  its  attack.  Sulphate  of  lime  is  not  altered  by  it. 

Molasses,  fruit,  cider,  vinegar,  etc.,  containing  more  or  less  acetic  acid,  have  been 
used  in  boilers  for  the  prevention  of  scale. 

Tannic  acid  as  well  as  acetic  acid  may  be  advantageously  used  to  purify  the  water  in 
tanks,  the  excess  of  acid  being  neutralized  by  carbonate  of  soda  before  the  water  is  fed 
into  the  boiler. 

It  has  also  been  proposed,  for  the  purification  of  water  in  tanks,  to  convert  the  earthy 
carbonates  into  soluble  chlorides  by  hydrochloric  acid,  and  to  neutralize  the  excess  of 
acid  by  filtration  through  carbonate  of  baryta  (witherite)  in  the  form  of  coarse  powder. 
The  soluble  chloride  of  barium  thus  formed  decomposes  the  siilphate  of  lime,  forming 
chloride  of  calcium  which  is  kept  in  solution,  and  insoluble  sulphate  of  baryta  which  is 
deposited.  (See  "  Steam  Boiler  Waters  and  Incrustations"  by  Dr.  J.  G.  Rogers,  Jour- 
nal of  the  Franklin  Institute,  1872.) 

When  boilers  have  been  fed  with  water  containing  a  large  quantity  of  organic  mat- 
ter, sewage,  bilge-water,  etc.,  it  has  been  found  that  they  remained  remarkably  free 
from  corrosion,  and  that  the  formation  of  scale  with  such  water  was  even  impossible. 
The  latter  effect  is  probably  due  to  the  mechanical  action  of  the  organic  matter  which 
envelops  the  solid  scale-producing  matter  as  soon  as  it  is  formed.  The  anti-corrosive 
effect  of  the  organic  matter  may  be  ascribed  to  its  absorption  of  the  free  oxygen  con- 
tained in  the  water. 


CHAPTER  XIX. 

BOILER-EXPLOSIONS. 

1.  Causes  of  Boiler-explosions. — Kupture  takes  place  in  a  boiler  either  when 
any  part  is  not  sufficiently  strong  to  resist  with  a  reasonable  margin  of  safety  the  stress 
produced  by  the  working  pressure  under  ordinary  conditions,  or  when  the  stress  ex- 
ceeds the  ultimate  strength  of  any  part  in  consequence  of  an  excessive  rise  of  pressure 
in  the  boiler,  or  in  consequence  of  great  variations  and  differences  of  temperature,  sud- 
den shocks,  weakening  of  plates  by  overheating,  or  similar  abnormal  conditions. 

The  weakness  of  a  boiler  may  be  due  to  the  faulty  design  of  its  bracing,  to  the  use 
of  inferior  material  or  to  injuries  received  by  it  in  the  processes  of  boilermaking,  to 
bad  workmanship,  and  to  gradual  deterioration  produced  by  the  various  causes  de- 
scribed in  chapter  xviii.  By  exercising  vigilance  in  supervising  the  building  of  a  boiler, 
and  by  conducting  with  intelligent  care  the  periodical  inspections  and  tests,  the  actual 
condition  of  a  boiler  may  be  known,  and  the  steam-pressure  which  it  can  bear  with 
safety  may  be  determined  accordingly.  The  original  cause  of  any  leak  or  sign  of  weak- 
ness should  always  be  determined  promptly  and  exactly,  and  removed  in  making  re- 
pairs, otherwise  deterioration  will  not  only  continue,  but  may  even  be  aggravated  by 
the  means  adopted  for  stopping  the  leak  or  strengthening  the  weak  place,  especially 
when  the  defect  is  produced  by  varying  bending  strains  near  the  attachment  of  braces 
or  the  laps  of  joints. 

Various  theories  have  been  proposed  to  account  for  the  instantaneous  generation  of 
excessive  pressure  within  steam  boilers  by  the  conjuncture  of  unusual  conditions  ;  seve- 
ral of  these  will  be  discussed  farther  on.  Such  theories  have  been  brought  forward 
especially  in  order  to  explain  the  frequent  occurrence  of  explosions  at  the  moment 
preparations  are  commenced  for  starting  the  engines  after  a  boiler  has  been  lying  with 
banked  fires  for  some  time. 

When  the  fires  are  burning  actively,  and  the  steam  is  allowed  to  accumulate  in  the 
boiler  by  keeping  the  stop  and  safety  valves  closed,  the  pressure  will  increase  with 
great  activity.  In  a  large  marine  boiler  of  ordinary  form  experimentally  exploded  at 
Sandy  Hook,  N.  J.,  in  1871,  the  pressure  rose  in  thirteen  minutes  from  29f  pounds  to 


443 


SBC.  1.  BOILER-EXPLOSIONS  443 

53J  pounds  per  square  inch ;  the  furnaces  contained  a  wood-fire,  and  the  water  in 
the  boiler  stood  15  inches  above  the  upper  row  of  tubes.  (See  section  5  of  the  present 
chapter.) 

A  gradual  excessive  accumulation  of  steam-pressure  is  always  due  to  mismanage- 
ment and  carelessness  ;  it  is,  however,  a  frequent  cause  of  boiler-explosions.  It  cannot 
take  place  when  the  boiler  has  a  safety-valve  of  sufficient  size,  properly  located  and  in 
working  order.  But  when  the  safety-valve  cannot  relieve  automatically  the  boiler  of 
an  excess  of  pressure,  the  latter  may  accumulate  to  a  dangerous  degree  rapidly  after 
steam  has  been  raised  and  the  engines  are  not  started  or  are  suddenly  stopped,  and 
more  gradually  when  the  engines  are  worked  slowly  or  when  the  boilers  are  kept  under 
steam  with  banked  fires.  The  danger  of  getting  an  overpressure  of  steam  in  the  boiler 
is  greatly  increased  when  the  steam-gauge  is  inoperative  or  gives  wrong  indications. 

The  following  circumstances  frequently  make  safety-valves  inoperative  in  practice : 
When  the  safety-valve  is  not  placed  directly  on  the  boiler,  but  on  the  steam-pipe  be- 
yond the  stop-valve,  the  latter  may  be  closed  and  shut  off  the  steam  from  the  safety- 
valve.  In  repairing  or  cleaning  the  boiler  the  workmen  sometimes  plug  up  the  aperture 
of  the  valve-chamber  from  inside  the  boiler,  or  put  a  blank  flange  between  the  safety- 
valve  and  the  escape-pipe  to  prevent  the  drip  of  hot  water  from  leaky  valves  ;  several 
cases  of  explosion  have  happened  in  consequence  of  the  neglect  of  removing  this  ob- 
struction before  the  boiler  was  closed  and  steam  was  raised.  In  cold  weather  the 
escape-pipe  may  be  obstructed  by  the  freezing  of  the  water  which  has  accumulated 
therein.  Safety-valves  are  sometimes  purposely  overloaded  and  tied  or  wedged  down 
by  reckless  attendants,  or  the  rise  of  the  valve  may  be  prevented  by  some  obstruction 
accidentally  placed  over  the  valve-chamber.  The  valve  may  stick  fast  in  consequence 
of  corrosion  or  of  the  accumulation  of  grease  and  dirt  at  the  articulations  of  the  lever 
and  in  the  guide-sleeve  of  the  stem  ;  or  it  may  be  prevented  from  rising  by  the  bending 
of  the  lever,  stem,  or  guide-spindle ;  or  the  too  closely  fitted  guide-feathers  may  be 
jammed  in  the  valve-chamber  in  consequence  of  distortion  or  unequal  expansion  caused 
by  irregular  strains  or  differences  of  temperature.  To  the  latter  cause  the  explosion  of 
the  boiler  of  the  British  armored  vessel  Thunderer  was  attributed. 

To  place  safety-valves  beyond  the  control  of  reckless  ignorance  and  carelessness 
boilers  are  provided  with  lock-up  safety-valves.  For  the  design,  construction,  and 
arrangement  of  safety-valves  see  section  11,  chapter  xv.  Safety-valves  should  be 
opened  by  hand  soon  after  steam  has  commenced  to  form,  and  from  time  to  time  after- 
wards while  steam  is  on  the  boilers,  to  make  sure  that  they  are  in  working  order. 

The  overheating  of  plates  may  be  caused  by  a  deficiency  of  water  in  the  boiler,  or 


444  STEAM  BOILERS.  CHAP.  XIX. 

by  the  formation  of  deposits  of  solid  matter  on  the  heating-surfaces,  or  by  the  accumu- 
lation of  steam  on  the  heating-surfaces.  The  overheated  parts  may  be  sufficiently 
weakened  to  give  way  at  once  at  the  ordinary  working  pressure  either  by  fracturing  or 
by  bulging ;  or  they  may  be  left  in  a  deteriorated  condition  after  cooling  down ;  or 
their  excessive  and  unequal  expansion  may  produce  injurious  strains  in  the  parts  with 
which  they  are  connected.  When  highly-overheated  plates  are  suddenly  partially 
cooled  by  coming  in  contact  with  water  their  local  contraction  may  produce  sufficiently 
severe  strains  to  rupture  them.  The  ways  in  which  rupture  or  severe  strains  are  pro- 
duced in  boilers  by  sudden  variations  of  temperature  have  been  described  in  section  3, 
chapter  xviii. 

Violent  shocks  are  liable  to  cause  rupture  in  boilers  which  are  in  a  strained  condition 
in  consequence  of  the  steam-pressure  within  them.  Such  shocks  may  be  produced  by 
heavy  weights  falling  on  the  boiler  or  by  the  collision  or  grounding  of  the  vessel.  The 
impact  of  the  water  carried  upward  by  the  rush  of  steam  when  the  safety-valve  or  a 
stop- valve  is  opened  suddenly  may  sometimes  be  sufficient  to  produce  rupture. 

Boilers  have  been  severely  jarred  by  the  detonation  of  inflammable  gases  which  had 
collected  in  their  flues.  When  a  boiler  is  kept  with  covered  banked  fires  and  tightly- 
closed  damper  the  gases  distilled  from  bituminous  coal,  not  being  able  to  escape  from 
the  flues,  may  form  in  them  a  detonating  mixture  with  the  atmospheric  air,  and,  under 
such  conditions,  an  explosion  may  occur  when,  by  uncovering  the  fires,  the  gases  are 
ignited.  More  or  less  severe  accidents  of  this  kind  have  occurred  with  stationary  boil- 
ers, but  they  cannot  take  place  where  dampers  are  not  employed,  as  is  usually  the  case 
in  marine  boilers. 

Successive  explosions  of  several  boilers  working  side  by  side  have  been  repeatedly 
observed,  and  may  be  explained  by  assuming  that  the  explosion  of  one  of  the  boilers 
produced  severe  jars  or  concussions  in  the  adjoining  ones,  or  that  the  latter  were  per- 
forated by  detached  pieces  from  the  exploded  boiler.  The  rupture  of  a  pipe  or  drum 
connected  with  several  boilers  may  be  the  cause  of  their  explosion.  In  a  war-steamer 
the  perforation  of  boilers  by  shot  or  splinters  in  action  is  a  dangerous  source  of  explo- 
sion. Locomotive  boilers  have  exploded  because  the  shell  was  pierced  by  a  broken 
connecting-rod,  or  because  the  steam-dome  was  carried  away  by  coming  in  contact  with 
a  tunnel  or  an  overhead  bridge. 

The  rupture  which  takes  place  in  a  boiler  may  be  only  of  a  local  character  and  not 
affect  the  strength  of  the  boiler  as  a  whole  ;  this  is  often  the  case  when  rivets  or  small 
portions  of  plate  are  blown  out  or  when  small  tubes  burst  or  collapse.  Or  the  damage 
done  to  any  part  may  cause  the  opening  of  seams  in  such  a  manner  as  to  allow  a  gradual 


SBC.  8.  BOILER-EXPLOSIONS.  445 

discliarge  of  the  steam,  thereby  relieving  the  boiler  of  an  overpressure.  In  these  cases 
the  principal  danger  consists  in  the  liability  to  scalding  by  hot  water  and  steam. 

The  rupture  of  a  boiler  is  called  an  explosion  when  it  causes  the  sudden  liberation 
of  large  masses  of  the  steam  and  water  confined  in  the  boiler,  by  which  means  a  dy- 
namic force  is  developed  which  aids  in  the  demolition  of  the  whole  structure  and  hurls 
detached  portions  with  great  violence.  This  will  take  place  when  the  rupture  deprives 
other  parts  of  the  boiler  of  an  essential  support,  and  thus  throws  additional  excessive 
strains  on  them,  as  in  the  case  of  broken  stays  or  braces,  and  rents  in  circular  shells  ;  or 
when  the  original  weakness  extends  over  a  large  portion  of  the  structure,  which  gives 
way  at  nearly  the  same  instant,  and  thereby  sets  free  suddenly  an  enormous  amount  of 
energy  stored  up  in  the  steam  and  heated  water. 

2.  Various  Theories  concerning  Boiler-explosions. — The  extreme  violence  of 
many  boiler-explosions  has  caused  the  very  general  impression  that  some  unusual, 
instantaneously -generated  forces  are  required  to  produce  them.  Although  it  has  been 
demonstrated  that  the  energy  stored  up  in  water  heated  to  a  temperature  corresponding 
to  the  ordinary  working  pressures  of  steam  boilers  is  more  than  sufficient  to  produce 
the  effects  of  the  most  violent  boiler-explosions,  and  although  it  has  been  repeatedly 
shown  by  direct  experiment  that  a  moderate  and  gradually-accumulated  steam-pressure 
in  a  weak  boiler  does  produce  all  the  phenomena  of  a  violent  explosion,  there  are  still 
many  advocates  of  special  theories  which  explain  these  phenomena  by  the  sudden  gene- 
ration of  abnormal  forces  within  the  boiler  in  consequence  of  the  concurrence  of  extra- 
ordinary circumstances.  It  is  of  the  gravest  importance  that  the  true  causes  of  every 
boiler-explosion  should  be  clearly  understood,  in  order  that  their  recurrence  may  be 
guarded  against.  The  tendency  to  ascribe  explosions  to  obscure  causes  rather  than  to 
regard  them  as  the  natural  results  of  conditions  which  can  be  prevented  by  intelligent 
care  exercised  in  the  design,  construction,  and  management  of  boilers,  has,  no  doubt,  its 
origin  in  the  desire  to  escape  responsibility  for  the  results  of  culpable  neglect,  and  has 
been  productive  of  much  mischief  by  engendering  carelessness  on  the  part  of  owners 
and  attendants  of  steam  boilers.  Before  accepting  any  theory  as  a  correct  explanation 
of  the  causes  of  an  explosion  it  is  not  sufficient  to  prove  that  the  circumstances  iipon 
which  the  theory  is  based  could  exist  in  the  case  in  question,  and  that  they  were  capa- 
ble of  producing  the  phenomena  observed,  but  it  must  be  shown  by  direct  evidence  that 
they  did  exist,  or  that  no  other  known  causes  could  or  were  likely  to  produce  the 
same  results. 

Little  need  be  said  about  the  theory  which  ascribes  boiler-explosions  to  an  electric 
discharge  ;  no  intelligent  explanation  has  eVer  been  given  of  the  supposed  generation  of 


446  STEAM  BOILERS.  CHAP.  XIX. 

electricity  of  sufficiently  high  tension  in  a  steam  boiler  to  produce  the  effects  of  a  violent 
explosion.  This  idea  probably  had  its  origin  in  an  imperfect  knowledge  of  the  fact 
that  a  current  of  steam  sometimes  exhibits  electrical  phenomena,  the  development  of 
electricity  being  solely  due,  as  Faraday  has  shown,  to  the  friction  of  the  suspended 
watery  particles  against  the  sides  of  the  orifice  through  which  the  steam  issues. 

Another  theory  assumes  the  possibility  of  the  formation  and  detonation  of  a  mix- 
ture of  hydrogen  and  oxygen  gases  in  a  steam  boiler.  The  hydrogen  set  free  in  conse- 
quence of  the  corrosion  taking  place  within  a  boiler,  and  the  free  oxygen  contained  in 
the  feed- water,  are  relatively  small  quantities  and  so  diffused  in  the  mass  of  steam  that 
they  cannot  form  an  explosive  mixture. 

At  a  meeting  of  the  American  Academy  of  Sciences  (1877)  it  was  shown  that  steam 
could  be  decomposed  by  simple  heat  into  the  constituent  gases  of  water — viz.,  hydro- 
gen and  oxygen.  The  apparatus  consisted  of  a  flask  in  which  water  was  heated,  a  tube 
conveying  the  steam  to  a  closed  platinum  crucible,  where  it  was  again  heated  by  a  spirit- 
lamp,  and  a  tube  which  carried  thence  the  superheated  steam  and  the  liberated  gases  to 
an  ordinary  pneumatic  trough,  where  the  mixed  gases  were  collected  in  a  test-tube 
while  the  steam  was  absorbed.  The  gases  thus  collected  were  exploded  by  a  lighted 
match.  The  heat  employed  was  a  little  over  ordinary  redness,  but  did  not  reach 
whiteness. 

In  order  that  a  detonating  mixture  of  oxygen  and  hydrogen  may  be  formed  by  a 
similar  process  in  a  steam  boiler,  a  considerable  portion  of  the  plates  enclosing  the 
steam-space  must  be  raised  to  a  bright-red  heat ;  then  the  steam  must  be  condensed  by 
the  injection  of  cold  water,  which  must  not  come  in  contact  with  the  red-hot  plates ; 
the  heat  of  the  latter  may  ignite  then  the  explosive  mixture  of  gases.  It  is,  however, 
highly  improbable  that  all  these  essential  conditions  will  be  fulfilled  in  a  steam  boiler, 
and  it  is  more  likely  that  rupture  will  take  place  in  consequence  of  the  weakened  con- 
dition of  the  red-hot  plates  or  of  their  sudden  cooling  by  the  injection  of  cold  water. 

Several  theories  have  been  proposed  to  explain  how  large  masses  of  water  might  be 
instantaneously  converted  into  steam  and  thus  prodiice  an  overpressure  in  a  boiler. 

It  has  been  assumed  that,  especially  when  the  feed- water  is  very  greasy,  the  phe- 
nomenon of  the  spheroidal  condition  of  water  might  be  produced  on  a  large  scale  in  a 
boiler,  and  that  when  a  large  mass  of  water  is  instantaneously  vaporized  under  these 
conditions  the  resulting  increase  of  pressure  and  the  impact  of  the  water  thrown  up 
against  the  shell  of  the  boiler  by  the  suddenly-formed  steam  would  be  sufficient  to  rup- 
ture the  boiler.  While  there  is  reason  to  believe  that  this  phenomenon  occurs  fre- 
quently on  a  small  scale  on  the  plates  forming*  the  furnace-crowns  and  the  combustion- 


Sic.  3.  BOILER-EXPLOSIONS.  447 

chamber,  and  increases  their  liability  to  deterioration,  there  is  no  evidence  that  large 
masses  of  water  have  ever  been  affected  similarly  in  a  boiler  in  such  a  manner  as  to 
generate  sufficiently  great  forces  to  produce  an  explosion. 

AYhen  water  is  deprived  completely  of  air  and  is  kept  perfectly  motionless  its  tem- 
perature may  be  raised  many  degrees  (according  to  Tyndall,  100°  Fahr.)  above  the  boil- 
ing-point ;  but  with  the  slightest  agitation  the  surplus  of  heat  in  the  water  is  expended 
in  the  sudden  formation  of  an  equivalent  mass  of  steam.  It  is  claimed  that  this  pheno- 
menon may  occur  in  a  steam  boiler  and  cause  its  destruction  by  an  instantaneous  in- 
crease of  pressure  and  by  the  impact  of  a  large  mass  of  water  thrown  violently  against 
the  walls  of  the  boiler  by  the  steam  formed  in  an  explosive  manner.  To  produce  this 
superheated  condition  of  the  water  the  boiler  must  be  supposed  to  have  been  standing 
for  a  long  time  undisturbed,  with  closed  valves  and  low  fires,  no  circulation  of  the 
water  taking  place  within  it.  The  sudden  opening  of  the  safety-valve  or  steam  stop- 
valve,  or  the  starting  of  the  feed-pump,  would  then  be  sufficient  to  produce  the  agitation 
of  the  water  which  causes  the  sudden  generation  of  steam.  In  the  case  of  a  marine 
boiler  the  vessel  likewise  must  lie  perfectly  motionless  during  the  period  of  superheat- 
ing. But  we  have  no  direct  evidence  that  these  conditions  have  ever  been  the  cause  of 
the  explosion  of  a  boiler,  and  it  is  very  doubtful  whether  a  large  mass  of  water  could 
be  highly  superheated  in  a  boiler  without  circulation. 

Another  theory  is  based  on  the  supposition  that  the  steam  in  the  boiler  has  become 
highly-superheated  in  consequence  of  the  overheating  of  the  surfaces  in  contact  with 
it ;  that  then,  by  some  means,  a  large  mass  of  water  is  carried  up  in  the  form  of  spray, 
and,  mingling  with  the  steam,  is  at  once  vaporized  by  the  surplus  of  heat  in  the  latter. 
The  thorough  mingling  of  a  large  mass  of  water  with  the  steam  is,  however,  not  easily 
effected  in  practice,  and,  even  in  extreme  cases,  the  whole  surplus  of  heat  in  superheated 
steam  would  not  be  sufficient  to  produce  a  considerable  increase  of  pressure  by  the 
vaporization  of  water. 

In  many  cases  the  vaporization  of  large  masses  of  water  coming  in  contact  with 
highly-overheated  plates  is  supposed  to  produce  the  sudden  increase  of  pressure  which 
is  regarded  as  the  cause  of  the  explosion.  A  large  amount  of  plate  raised  to  a  red  heat 
might,  no  doubt,  contain  a  sufficient  quantity  of  heat  to  produce  this  effect ;  but  gene- 
ral experience  as  well  as  direct  experiment  have  demonstrated  the  fact  that  water  thrown 
on  a  red-hot  plate  does  not  absorb  heat  with  sufficient  rapidity  to  generate  suddenly  a 
large  quantity  of  steam.  Several  experiments  were  made  by  the  Manchester  Steam- 
users'  Association  to  test  this  theory.  Some  small  empty  boilers  were  made  red  hot 
and  water  was  forced  into  them,  but  in  every  case  the  boiler  failed  to  explode.  In  most 


4A8  STEAM  BOILERS.  CHAP.  XIX. 

boilers  the  feed-entrance  is  near  the  bottom,  and  when  the  feed  is  turned  on  the  water 
will  rise  gradually  up  to  the  overheated  plates  and  will  not  be  scattered  over  them. 
Severe  overheating  of  plates  in  a  boiler  frequently  opens  the  riveted  seams,  and  thus 
offers  a  means  of  escape  to  the  steam  and  prevents  an  excessive  accumulation  of 
pressure. 

In  nearly  every  case  in  which  severe  overheating  of  portions  of  the  boiler  has  taken 
place  previous  to  an  explosion  it  is  reasonable  to  suppose  that  the  loss  of  strength  in 
the  overheated  plates,  or  their  strained  condition  when  suddenly  cooled  off,  woiild  be 
sufficient  to  cause  rupture  even  with  the  ordinary  working  pressure  ;  and  while  an  in- 
crease of  pressure  produced  by  the  sudden  vaporization  of  a  certain  quantity  of  water 
and  a  violent  projection  of  water  may  have  occurred  simultaneously  and  to  a  certain  de- 
gree intensified  the  disruptive  force,  it  is  the  weakened  condition  of  the  boiler  which 
must  be  regarded  as  the  primary  cause  of  the  explosion. 

Assuming  that  a  boiler  explodes  either  in  consequence  of  a  sudden  reduction  of  its 
strength  or  of  a  gradually -accumulated  overpressure,  rupture  commences  at  the  weakest 
part  and  continues,  following  the  lines  of  least  resistance,  in  such  parts  as  have  been  re- 
duced in  strength  or  are  left  insufficiently  supported  after  the  primary  fracture.  De- 
tached portions  of  the  boiler  are  projected  with  more  or  less  violence,  impelled  by  the 
unbalanced  force  of  steam  pressing  on  their  surfaces,  and  a  force  of  corresponding  mag- 
nitude reacts  on  the  opposite  walls  of  the  boiler.  The  steam  expands  to  atmospheric 
pressure,  and  a  portion  of  the  heated  water  vaporizes  as  the  superincumbent  pressure 
diminishes.  The  steam  suddenly  generated  in  the  body  of  heated  water  carries  along  a 
mass  of  water,  the  impact  of  which  assists  in  the  work  of  destruction.  . 

The  rapidity  with  which  these  consecutive  effects  are  produced  depends  on  the 
nature,  location,  and  extent  of  the  fractures.  The  weight  and  temperature  of  the  water 
and  steam  determine  the  amount  of  energy  stored  up  in  a  boiler ;  but  the  violence  of 
an  explosion,  or  the  work  done  in  exploding  a  boiler,  depends  greatly  on  the  rapidity 
with  which  the  energy  stored  up  in  a  boiler  is  liberated. 

In  discussing  one  of  the  experimental  steam-boiler  explosions  at  Sandy  Hook,  N.  J., 
in  1871,  Professor  R.  H.  Thurston  presented  the  following  calculations  of  the  energy 
stored  up  in  the  boiler  and  of  the  work  done  by  the  liberated  forces : 

"  The  steam  boiler  referred  to  weighed  40,000  Ibs.,  and  contained  about  30,000  Ibs.  of 
water  and  150  Ibs.  of  steam,  all  of  which  had  a  temperature  of  301°  Fahr.,  when,  at  the 
moment  before  explosion,  the  steam-pressure  was  53£  pounds  above  that  of  the  atmos- 
phere. 

"When  the  explosion  took  place  the  whole  mass  at  once  liberated  its  heat,  until 


SEC.  2.  BOILER-EXPLOSIONS.  449 

it  had  cooled  down  to  the  temperature  of  vapor  under  the  pressure  of  the  atmos- 
phere. 

"In  this  act  the  water  gave  off  30,000  x  89°  =  2,670,000  British  thermal  units,  and 
the  steam  lost  the  difference  between  its  total  heat  at  301°  and  that  of  212°  Fahr.,  or 
150  x  27. 2°  =  4, 080  thermal  units.  The  sum  2, 670, 000  +  4, 080  =  2, 674, 080  thermal  units 
has  an  equivalent  in  mechanical  energy  of  2,674,080  X  772  =  2,064,389,760  foot-pounds, 
and  this  was  sufficient  to  have  raised  the  whole  boiler  and  contents,  weighing  70, 000  Ibs., 
to  a  height  of  29,491.282  feet — more  than  five  miles.  This  represents  the  maximum 
possible  effect. 

"  The  least  effect  would  have  been  produced  had  the  liberation  of  heat  and  the  pro- 
duction of  additional  quantities  of  steam,  within  the  mass  of  water  and  at  its  surface, 
been  so  sluggish  as  to  have  given  no  assistance  in  propelling  the  fragments  of  the  rup- 
tured boiler,  the  whole  destructive  work  being  done  by  the  simple  expansion  of  the 
steam  which  filled  the  steam-spaces. 

"  The  total  amount  of  mechanical  energy  set  free  from  the  steam  alone  was  4,080  X 
772  =  3, 149,760  foot-pounds,  or  sufficient  to  raise  the  whole  boiler  through  a  space  of  78.74 
feet  and,  water  included,  44.99  feet.  Owing  to  the  greater  inertia  of  the  lower  part  of 
the  boiler,  and  particularly  of  its  inelastic  burden  of  water,  the  principal  part  of  this 
work  was  undoubtedly  performed  upon  the  upper  portion  and  steam-chimney  of  the 
boiler,  weighing  probably  6,000  Ibs.  ;  and,  if  entirely  expended  in  this  direction,  the 
work  thus  done  was  equivalent  to  raising  this  6,000  Ibs.  to  a  height  of  525  feet. 

"This  latter  case  is  capable  of  treatment  in  quite  a  different  way  from  the  above. 
As  the  boiler  was  completely  torn  in  pieces,  the  steam  must  have  expanded  pretty 
equally  in  all  directions,  except  where  checked  in  its  downward  movement,  and  may 
probably  be  treated  as  if  forming  a  rapidly-expanding  hemisphere  of  vapor,  its  centre 
being  in  the  steam-space  of  the  boiler. 

"The  expansion  of  this  hemisphere  would  have  continued  until  the  tension  of  the 
steam  was  rediiced  to  that  of  the  surrounding  atmosphere,  and  would  have  continued 
through  a  mean  distance,  as  given  by  an  approximate  estimate,  of  4.5  feet.  The  mean 
pressure  would  be  25  pounds  above  the  atmosphere  nearly. 

"  The  area  of  cross-section  of  the  steam-drum  was  4,071  square  inches,  and  4,071  X 
25  X  4.5  =  457,987.5  foot-pounds,  the  amount  of  work  done  in  its  projection. 

"  The  weight  of  the  steam-drum,  which  was  J  inch  thick,  6  feet  diameter,  and  8  feet 
8  inches  high,  was,  with  its  braces,  2,500  Ibs.,  and  457,987.5  -f-  2,500  =  183.2,  the  height 
in  feet  to  which  the  drum  might  have  been  thrown  by  the  simple  expansion  of  the  con- 
fined steam.  In  fact,  the  steam-drum  had  attached  to  it,  when  found  after  the  explo- 


450  STEAM  BOILERS.  CHAP.  XIX. 

sion,  a  considerable  part  of  the  boiler-top,  which,  being  comparatively  light  and  being 
acted  upon  by  similar  pressures,  must  have  considerably  accelerated  rather  than 
retarded  its  ascent. 

"The  actual  height  of  ascent  of  this  piece  was  variously  estimated  by  the 
spectators  at  from  200  to  400  feet."  (Journal  of  the  Franklin  Institute,  March, 
1872.) 

3.  Phenomena  of  Boiler-explosions. — "When  a  boiler  gives  way  from  over- 
pressure or  sudden  contraction  a  rent  may  be  formed  or  a  piece  of  plate  blown  out. 
The  former  is  the  most  usual  manner  of  yielding  ;  but  in  both  cases  it  will  depend  upon 
the  strength,  nature,  and  arrangement  of  the  material  bounding  the  initial  fracture,  as 
well  as  its  position,  and  also  upon  the  pressure,  temperature,  and  amount  of  water 
and  steam  in  the  boiler,  whether  the  contents  will  gradually  escape  through  the  open- 
ing already  made,  or  whether  in  their  violent  rush  they  will  increase  the  extent  of 
opening,  and  make  it  easy  for  the  steam  behind  to  tear  the  boiler  into  several  pieces 
and  cause  a  violent  explosion. 

"Now,  to  make  this  more  clear,  we  shall  first  consider  the  influence  of  the  position 
of  fracture.  Many  cases  have  occurred  of  manhole-lids  on  the  crowns  of  horizontal 
boilers  being  blown  aloft  either  from  defect  of  fastening  down  or  defect  of  material. 
When  the  manhole  is  properly  fortified  with  a  mouth-piece  or  ring  the  cover  is  pro- 
jected aloft,  the  contents  gradually  escape  through  the  hole,  and  the  boiler  is  left  on  its 
seat  (if  this  be  sufficiently  strong  to  withstand  the  recoil),  and  probably  no  further  dam- 
age is  done,  except  to  the  boiler-house  roof.  Should,  however,  the  same  accident 
happen  to  a  manhole-cover  underneath  the  boiler,  placed  near  the  ground,  the  effect  will 
be  very  different,  and  it  will  depend  upon  the  weight  of  the  boiler  and  water  contained, 
size  of  manhole,  pressure  of  steam,  and  distance  of  aperture  from  the  ground  whether 
the  boiler  and  its  contents  will  be  merely  raised  a  little  from  its  seat,  or  whether  it 
will  be  shot  aloft  like  a  rocket  by  the  unbalanced  pressure  on  the  discharge  of  steam. 
If  the  manhole  were  in  the  side  of  a  vertical  boiler,  and  near  the  top,  the  blowing-off 
of  the  lid  into  an  open  space  in  front  would  probably  topple  over  the  boiler  if  it 
were  not  well  supported. 

"Again,  if  the  manhole  in  our  first  case  were  without  any  provision  for  strength- 
ening the  plate  surrounding  it,  and  if  the  edges  of  the  plate  were  reduced  in  strength 
by  fractures  or  by  corrosion  and  wear,  the  rush  of  steam  and  water  on  the  lid  blow- 
ing off  would  probably  start  a  rent  in  the  shell,  which  a  high  pressure  within  the  boiler 
would  continue  along  the  lines  of  least  resistance,  and  the  result  would  be  a  violent 
explosion,  the  severed  plates  being  carried  in  different  directions. 


SBC.  3.  BOILER-EXPLOSIONS.  451 

"The  remarks  respecting  the  blowing-away  of  the  manhole-cover  apply  also  to 
the  case  of  a  piece  of  plate  being  blown  out."  (Wilson.) 

When  a  single  stay  gives  way  in  a  boiler  there  is  a  strong  probability  that  the 
adjoining  stays  will  also  give  way  in  rapid  succession  on  account  of  the  greatly-in- 
creased load  thrown  on  them.  The  unsupported  plate  bulges  out  and  finally  tears, 
usually  through  the  line  of  rivet-holes  in  the  seams.  Unless  braces  are  much  reduced 
in  sectional  area  by  corrosion,  their  weakest  part  is  generally  at  the  weld  or  in  their 
fastenings.  The  angle-irons  to  which  braces  are  attached  tear  frequently  through  the 
rivet  or  bolt  holes.  When  the  bulging  of  plates  exceeds  a  certain  limit  the  stay-bolts 
are  drawn  through  them,  especially  when  they  are  simply  screwed  in  or  secured  by 
riveted  heads. 

When  large  flues  collapse  without  fracturing  to  a  great  extent  the  steam  or  water 
issuing  through  the  cracks  or  opened  seams  may  reduce  the  pressure,  or,  by  putting 
out  the  fires,  check  the  increase  of  pressure  sufficiently  to  avert  an  explosion.  If  the 
fracture  is  of  larger  extent  there  is  great  danger  of  scalding  by  hot  water  and  steam  ; 
the  furnace-doors  will  be  blown  open  and  the  fire  scattered  over  the  fire-room  floor. 
If  a  flue  is  ruptured  to  such  an  extent  that  it  no  longer  acts  as  an  efficient  stay  for 
the  plates  to  which  it  is  attached,  a  violent  explosion  will  be  the  probable  result, 
the  ends  of  the  boiler  being  blown  away  in  opposite  directions. 

Similar  results  will  be  produced  when  a  number  of  tubes  are  either  fractured  or 
pulled  out  of  the  tube-plates. 

The  reaction  of  the  steam  and  water  issuing  from  the  collapsed  furnace-crown  of 
a  locomotive  boiler  or  of  a  vertical  fire-tube  boiler  frequently  sends  the  boiler  into  the 
air  to  a  great  height  like  a  rocket. 

An  extensive  rupture  in  a  cylindrical  boiler  generally  results  in  a  violent  explosion 
and  the  total  destruction  of  the  boiler,  because  its  various  parts  are  connected  in  such 
a  manner  as  to  form  essential  supports  for  each  other.  On  the  contrary,  large  portions 
of  the  flat  stayed  surfaces  of  a  rectangular  boiler  may  give  way  without  seriously 
weakening  the  rest  of  the  boiler. 

The  violent  explosion  of  the  large  rectangular  boiler  of  the  British  armored  vessel 
Thunderer,  in  1876,  commenced  with  the  giving- way  of  some  stay-bolts  which  tied  the 
boiler-front  to  the  uptake.  The  whole  front  above  the  smoke-connections  was  torn  off 
the  shell  through  the  lines  of  rivet-holes  in  the  seams  and  thrown  down,  and  the 
portion  of  the  uptake  to  which  the  front  was  stayed  was  torn  and  bent  out  of  shape  ; 
but  the  rest  of  the  boiler  was  uninjured. 

The  reports  and  papers  published  by  the  Hartford  Steam-boiler  Inspection  and  In- 


452  STEAM  BOILERS.  CHAP.  XIX. 

surance  Company  contain  descriptions  and  illustrations  of  several  instructive  cases  of 
explosion  of  locomotive  and  marine  boilers,  in  which  the  semi-cylindrical  top  gave  way, 
rupture  commencing  at  and  following  a  line  of  grooving  near  the  horizontal  seams.  In 
one  case  the  whole  semi-cylindrical  top  was  blown  off,  fracture  taking  place  almost 
simultaneously  at  both  sides  through  lines  of  grooving  near  the  horizontal  seams  which 
joined  the  top  to  the  lower  rectangular  part  of  the  shell,  and  extending  through  the 
transverse  seams  connecting  the  top  to  the  front  plate  and  to  the  cylindrical  barrel  of 
the  boiler. 

In  other  cases  a  piece,  extending  nearly  the  whole  length  of  the  semi-cylindrical  top, 
was  torn  off  on  one  side  of  the  boiler.  The  fracture  followed  likewise  a  line  of  hori- 
zontal grooving  near  a  seam,  and  extended  in  a  transverse  direction  to  lines  where  the 
shell  was  strengthened  by  stays  or  by  the  flanges  of  steam-domes,  the  detached  pieces 
bending  over  on  these  lines  as  on  hinges.  In  one  case  the  piece  thus  torn  off  the  side 
of  a  locomotive  boiler  was  about  5£  feet  long  and  1£  feet  wide,  and  had  an  area  of 
nearly  7£  square  feet.  The  pressure  on  this  area  was  but  a  little  less  than  70  tons  at 
the  pressure  of  130  pounds  per  square  inch.  The  reaction  of  the  force  set  free  by  the 
rupture  overturned  the  locomotive. 

When  a  cylindrical  shell  gives  way  at  a  longitudinal  seam,  or  by  tearing  through  a 
longitudinal  line  of  weakness  produced  by  corrosion  or  grooving,  the  fracture  may  be 
confined  to  a  single  plate,  and,  by  continuing  through  the  circumferential  seams,  detach 
the  belt  of  which  it  forms  part  from  the  shell,  or  the  longitudinal  fracture  may  con- 
tinue through  several  belts.  The  latter  is  generally  the  case  when  the  longitudinal 
seams  of  adjoining  plates  are  in  the  same  line.  When  they  break  joint  the  rent  ex- 
tends sometimes  in  a  diagonal  direction  through  adjoining  plates  till  it  strikes  again  a 
longitudinal  seam,  along  which  it  continues.  As  the  fracture  extends  in  a  transverse 
direction  after  the  longitudinal  rupture  has  taken  place,  the  cylindrical  plates  are  flat- 
tened out,  and  in  this  manner  the  rivet-heads  in  circumferential  seams  are  frequently 
torn  off.  When  the  longitudinal  rupture  takes  place  near  the  bottom  of  the  boiler  the 
detached  plates  will  probably  be  thrown  some  distance  ;  but  when  this  line  of  fracture 
is  near  the  top  the  plates  may  be  found  in  nearly  their  original  location.  There  is  a 
strong  probability  that  when  a  circumferential  belt  of  plates  has  been  torn  off  a  cylin- 
drical shell,  the  two  ends  of  the  boiler  will  separate  and  will  be  thrown  a  greater  or  less 
distance  in  opposite  directions.  But  in  some  cases,  when  the  two  ends  are  tied  together 
strongly  by  their  braces,  stays,  and  flues,  or  when  the  destructive  forces  spend  them- 
selves promptly  through  the  vent  made  by  the  original  fracture,  the  boiler  remains 
otherwise  uninjured  and  is  not  moved  from  its  seat. 


SEC.  4  BOILER-EXPLOSIONS.  453 

In  the  case  of  the  boiler-explosion  on  the  steamer  Westfield,  in  the  harbor  of  New 
York,  in  1871,  rupture  commenced  at  one  side  of  the  cylindrical  shell  of  the  boiler 
along  a  horizontal  line  of  grooving.  The  fracture  extended  through  the  width  of  one 
plate  and  continued  through  the  transverse  seams,  detaching  one  belt  from  the  rest  of 
the  shell  and  flattening  it  out.  This  portion  of  the  shell  was  found  lying  directly  op- 
posite the  original  position  in  the  boiler  before  the  explosion.  The  front  and  the  back 
of  the  boiler  had  separated  and  were  thrown  some  distance  in  opposite  directions. 

4.  Investigation  of  Boiler-explosions. — "  In  investigating  the  cause  of  a  com- 
plicated explosion  the  relative  weights,  positions,  shapes  of  the  scattered  pieces,  and 
the  direction  taken  by  them  must  first  of  all  be  carefully  noted,  and  their  original  posi- 
tions in  the  boiler  be  assigned  to  them,  along  with  the  positions  of  the  different  mount- 
ings, manner  of  staying,  and  absence  or  presence  of  means  for  strengthening  domeholes, 
manholes,  tubes,  combustion-chambers,  etc.  The  original  shape  of  the  shell  and  large 
flue-tubes  should  be  ascertained  as  accurately  as  possible.  The  primary  rent  is  then  to 
be  sought  for.  In  many  cases  the  direction  taken  by  the  heavier  pieces  is  a  guide  to 
this,  as  the  fractured  plates,  if  free  to  move,  will  shoot  off,  the  light  pieces  along  with 
and  in  the  direction  of  the  first  rush  of  steam,  and  the  heavier  pieces  in  an  opposite 
direction. 

"That  this,  however,  is  not  always  the  case  is  obvious  ;  as,  for  instance,  when  the 
boiler  turns  over  before  separating,  or  where  the  direction  a  piece  of  the  shell  would 
take,  if  free  to  move,  is  changed  by  part  of  it  clinging  for  a  time  to  the  larger  mass  to 
which  it  may  be  attached. 

"All  the  edges  of  the  plates  and  angle-irons  along  the  lines  of  fracture  should  be 
carefully  examined  in  search  of  weak  places,  such  as  thinness  caused  by  grooving  and 
corrosion,  external  and  internal,  wasting  of  rivet-heads,  defective  rivet-holes,  insuffi- 
cient lap,  old  flaws  and  fractures,  patching  and  other  signs  of  repair,  indications  of 
softening  or  deterioration  by  overheating,  condition  of  low-water  indicating  apparatus, 
safety-valves,  and  pressure-gauges. 

"A  close  examination  of  the  shape  of  the  rivet-heads  and  of  the  shapes  and  sizes  of 
the  plates  and  arrangement  of  seams  throughout  the  boiler  will  usually  lead  to  detec- 
tion of  repairs  when  these  are  not  obvious  at  first  sight.  The  color  and  nature  of  the 
fractures,  and  whether  they  be  short  or  jagged,  are  the  only  guides  to  the  length  of 
time  they  have  existed  and  how  they  are  produced. 

"Overheating  from  shortness  of  water  usually  declares  itself  by  the  bulging  and 
buckling  of  the  plates,  by  breaking  off  the  incrustation  on  one  side,  and  by  producing 
a  burnt  appearance,  along  with  removal  of  soot,  etc.,  on  the  other  side,  by  the  starting 


454  STEAM  BOILERS.  CHAP.  XIX. 

of  joints  and  melting  of  fusible  plugs,  and  in  furnace- tubes  also  by  forming  corruga- 
tions parallel  with  the  ring-seams.  These  corrugations  are  produced  by  the  excessive 
expansion  of  the  plates  at  the  part  where  they  occur.  .  .  . 

"One  or  more  of  the  defects  above  indicated  will  in  most  cases  be  found  to  be  the 
cause  of  explosion,  which  may  have  occurred  at  the  ordinary  working  pressure.  But  if 
no  such  defects  can  be  found,  and  the  calculated  strength  of  the  boiler  be  sufficient  for 
the  alleged  working  or  blowing-off  pressure,  the  condition  of  the  safety-valves,  levers, 
weights,  springs,  double-eyes,  pipes,  or  branches  must  be  still  more  closely  enquired1 
into  and  the  strength  of  the  plates  at  fractures  carefully  tested.  The  alleged  blowing- 
off  pressure  must  be  carefully  checked  by  calculating  the  weight  upon  the  valve,  and 
the  accuracy  of  the  pressure-gauge  as  well  as  its  condition  should  be  ascertained,  and 
anything  else  suggested  by  the  nature  of  the  case  that  may  throw  light  upon  the  man- 
ner in  which  the  overpressure  has  been  brought  about."  (  Wilson.) 

5.  Experimental  Steam-boiler  Explosions. — A  series  of  instructive  experi- 
ments on  the  explosion  of  steam  boilers  was  made  by  the  United  Railroad  companies 
of  New  Jersey,  under  the  direction  of  Francis  B.  Stevens,  at  Sandy  Hook,  N.  J.,  in 
November,  1871,  in  the  presence  of  a  number  of  prominent  engineers. 

The  first  experiment  was  made  with  a  boiler  of  the  type  represented  in  figure  2, 
Plate  XXI.  It  was  28  feet  long,  and  the  cylindrical  portion  of  the  shell  was  6  feet  6 
inches  in  diameter  and  of  iron  a  full  quarter-inch  thick.  The  boiler  had  been  thirteen 
years  in  use,  and  the  last  inspector's  certificate  had  allowed  40  pounds  of  steam  to  be 
carried  in  it.  Before  the  final  trial  it  had  been  repaired  and  tested  by  hydrostatic 
pressure  to  82  pounds  per  square  inch  without  fracture,  and  then  had  been  subjected 
to  a  steam-pressure  of  60  pounds  per  square  inch  without  fracture. 

On  its  final  trial  a  heavy  wood-fire  was  built  in  the  furnaces,  the  water  standing  12 
inches  deep  over  the  flues.  The  pressure  rose  rapidly  until  it  reached  90  pounds,  when 
leaks  appeared  in  all  parts  of  the  boiler,  and  at  93  pounds  a  rent  at  the  rear  of  the 
steam-drum,  where  it  joined  the  shell,  became  so  great  that  the  steam  passed  off  more 
rapidly  than  it  was  formed.  After  the  fires  were  extinguished  it  was  found  that  at  the 
point  where  the  steam-drum  joins  the  shell  the  latter  had  been  drawn  downwards,  and 
each  crown-sheet,  originally  flat  and  stayed  to  the  roof  of  the  shell,  had  been  forced 
down  and  bulged,  to  an  extent  of  about  2  inches,  between  two  rows  of  the  stays  referred 
to,  pulling  the  outside  shell  with  it  away  from  the  lower  sheet  of  the  vertical  steam- 
drum,  thus  opening  a  seam,  venting  the  boiler,  and  preventing  an  explosion. 

The  second  experiment  was  made  on  a  flat  rectangular  box,  6  feet  long,  4  feet  high, 
and  4  inches  wide  over  all,  made  to  represent  the  water-leg  of  a  boiler.  The  two  side- 


SEC  5. 


BOILER-EXPLOSIONS.  455 


plates  were  of  the  best  flange  fire-box  iron,  ^  inch  thick.  They  were  held  together  by 
a  single  row  of  rivets  at  their  edges,  passing  through  a  frame  made  of  wrought-iron 
bars  3f  inches  wide  and  2  inches  deep,  mitred  at  their  ends.  The  side-plates  were 
braced  together  every  8f  inches  one  way  and  9^  inches  the  other  way  of  their  surfaces 
by  screw  stay-bolts  of  1£  inches  diameter  with  their  ends  slightly  riveted  over.  This 
box  had  been  subjected  to  a  hydrostatic  pressure  of  138  pounds  per  square  inch  without 
fracture,  and  to  a  steam-pressure  of  102  pounds  per  square  inch. 

This  box  was  set  on  one  edge  between  walls  of  brick  masonry,  and  it  was  filled  with 
water  up  to  about  five-sixths  of  its  height ;  a  strip  at  the  top  of  the  box  about  15  inches 
wide  projected  beyond  the  masonry.  The  enclosed  portion  of  the  box  was  heated  by 
two  small  furnaces  in  which  wood-fires  were  built.  The  pressure  rose  in  33  minutes 
from  0  to  165  pounds  per  square  inch. 

"  When  the  pressure  reached  165  pounds  to  the  square  inch  the  box  exploded  with  a 
loud  report,  completely  demolishing  the  brickwork  by  which  it  was  enclosed.  The  two 
sides  were  hurled  in  exactly  opposite  directions,  and  to  about  equal  distances,  at  right 
angles  to  their  surfaces.  The  fracture  had  occurred  in  one  plate  only,  and  was  along 
the  whole  riveted  seam  joining  it  to  the  frame.  For  a  large  part  of  the  length  of  the 
seam  this  plate  was  torn  out  between  the  rivets,  and  for  the  remaining  part  the  rivets 
were  sheared.  The  other  plate  was  not  fractured  nor  were  the  bars  of  the  frame  broken ; 
the  plate  and  the  frame  remained  riveted  together,  but  not  uninjured,  all  the  bars  of 
the  latter  being  bent  considerably  inwards,  forming  an  irregular  curve  of  from  four  to 
six  inches  versed-sine.  Both  plates  were  bulged  out  irregularly,  so  as  to  be  about  nine 
inches  dishing,  and  the  bulging  took  place  near  the  bars.  Not  one  of  the  bolts  was 
broken,  and  neither  the  threads  upon  their  ends  nor  the  threads  in  the  plate  were 
stripped  or  injured,  but  the  slight  riveting-over  of  the  ends  of  the  bolts  was  broken  off 
in  all  of  them."  .  .  .  "Between  the  bolts  there  was  a  small  permanent  stretching  of 
the  plates,  giving  each  space  between  the  bolts  a  slightly  dishing  or  bulged  form  in 
addition  to  the  general  bulging  of  the  plates,  thus  forming  a  system  of  secondary  bulges, 
as  it  were,  and  around  every  bolt  both  plates  were  strongly  marked  by  a  congeries  of 
circular  crispations."  (See  '  Report  of  United  States  Naval  Engineers '  and  Journal 
of  the  Franklin  Institute,  1872,  Nos.  1  and  2.) 

The  following  account  of  the  third  experiment  is  taken  from  the  report  of  the  board 
of  United  States  naval  engineers,  consisting  of  B.  F.  Isherwood,  E.  S.  De  Luce,  and 
Sidney  Albert,  Chief  Engineers  United  States  Navy,  detailed  by  the  Secretary  of  the 
Navy  to  witness  these  experiments : 

"  The  boiler  that  was  exploded  during  this  experiment  was  built  by  T.  F.  Secor  in 


456  STEAM  BOILERS.  CHAP.  XIX. 

1845,  and  taken  out  of  the  steamboat  Bordentown  in  August  last,  after  having  been  25 
years  in  use.  When  taken  out  the  inspector's  certificate  allowed  it  to  be  worked  with 
a  pressure  of  30  pounds  per  square  inch.  It  was  a  horizontal  fire-tube  boiler,  with  the 
tubes  returned  immediately  above  the  furnace  and  combustion-chamber. 

"  It  had  but  one  furnace,  and  that  was  11  feet  5  inches  in  width,  with  grate-bars  7 
feet  in  length.  The  top  of  the  furnace  and  the  top  of  the  combustion-chamber  were 
flat,  and  braced  to  the  flat  top  of  the  shell  above  them  by  rectangular  braces  2  inches 
by  J  inch  in  cross-section,  placed  17  inches  apart  crosswise  the  boiler  and  12  inches  apart 
lengthwise  the  boiler,  each  brace  holding  a  flat  surface  of  204  square  inches,  to  which  it 
was  attached  by  crow-feet  so  arranged  that  the  flat  surface  between  the  sustaining  rivets 
was  12  inches  square.  The  flat  water-spaces  were  braced,  at  intervals  of  8  inches  in  one 
direction  and  12  inches  in  the  other,  by  1-inch  diameter  screw-bolts,  each  of  which  held 
a  flat  surface  of  96  square  inches.  The  iron  plates  of  the  boiler  were  a  large  J  inch 
thick.  .  .  . 

"  The  shell  of  the  boiler  was  rectangular,  with  the  exception  that  the  vertical  sides 
were  joined  to  the  flat  top  by  quadrantal  arcs  of  37  inches  radius.  All  the  seams  were 
single-riveted.  Upon  the  centre  of  the  top  of  the  boiler  was  a  cylindrical  steam-drum 
of  6  feet  diameter  and  8  feet  8  inches  height.  The  flat  water-space  at  the  front  of  the 
furnace  was  4J  inches  wide,  and  that  at  the  back  end  of  the  boiler  was  5  inches  wide, 
including  thicknesses  of  metal.  The  width  of  the  boiler  was  12  feet  2  inches,  its  length 
15  feet  5  inches,  and  its  height,  exclusive  of  the  steam-drum,  was  8  feet  6  inches. 

"  The  shell  was  braced  very  unequally.  Each  upper  brace,  1£  inches  large  in  diame- 
ter, sustained  the  pressure  upon  a  surface  28  by  12  inches,  or  336  square  inches  ;  and 
each  rectangular  vertical  brace  adjacent  to  the  sides,  2  inches  by  J  inch  cross-section, 
sustained  the  pressure  upon  a  surface  19  by  12  inches,  or  228  square  inches  ;  these  were 
the  weakest  places. 

"  The  following  were  the  grate  and  the  water-heating  surfaces  of  the  boiler : 

Grate-surface 79|£  sq.  feet. 


Heating-surface  in  furnace 180 

"             "in  combustion-chamber  and  back-connec- 
tion        103 

"  «     in  tubes 2,171 

"  "     in  uptake 64        " 


Total  heating-surface 2,518 


SEC.  5. 


BOILER-EXPLOSIONS. 


457 


"  On  the  3d  of  September  last  this  boiler  was  subjected  to  a  hydrostatic  pressure  of 
60  pounds  per  square  inch,  when  twelve  crow-feet  gave  way.  After  being  repaired  it 
was  again  subjected  on  the  4th  of  November  last,  when  erected  at  Sandy  Hook,  to  a 
hydrostatic  pressure  of  69  pounds  per  square  inch,  which  it  bore  without  fracture  ;  and 
on  the  16th  of  November  last  it  was  subjected  to  a  steam-pressure  of  45  pounds  per 
square  inch,  which  it  also  sustained  without  fracture. 

"  The  fuel  used  in  the  experiment  was  wood,  and  the  water-level  in  the  boiler  was 
15  inches  above  the  highest  point  of  the  tubes.  When  the  fire  had  been  brought  to 
steady  action  the  pressure  of  the  steam  gradually  increased  at  the  following  rate,  com- 
mencing with  the  pressure  of  29i-  pounds  per  square  inch : 


Time  P.M. 
Hours.               Minutes. 

Steam-pressure  in  pounds  per 
square  inch  above    atmosphere. 

Time  P.M. 
Hours.                 Minutes. 

Steam-  pressure  in  pounds  per 
square  inch   above  atmosphere. 

12 

21 

29* 

12 

3<> 

46* 

12 

23 

33^ 

12 

31 

48i 

12 

25 

37i 

12 

32 

So 

12 

27 

4i 

12 

33 

52 

12 

29 

44i 

12 

34 

53i 

"At  the  pressure  of  50  pounds  per  square  inch  some  of  the  braces  in  the  boiler  gave 
way  with  a  loud  report,  and  when  the  pressure  of  53£  pounds  was  reached  the  boiler 
exploded  with  terrific  violence.  The  steam-drum  and  a  portion  of  the  shell  attached  to 
it,  forming  a  mass  of  about  three  tons  weight,  were  hurled  to  a  great  height  in  the  air 
and  fell  to  the  earth  at  about  450  feet  from  the  original  position  of  the  boiler,  crushing 
several  trees  in  their  fall.  Two  other  large  fragments  fell  at  less  distances,  while  smaller 
ones  were  thrown  much  farther.  Almost  the  whole  of  the  boiler  was  literally  torn  into 
shreds,  which  were  scattered  far  and  wide,  the  only  portion  remaining  where  the  boiler 
had  been  being  the  tubes.  These,  though  considerably  distorted,  were  otherwise  unin- 
jured. Both  tube-plates  had  been  blown  from  the  tubes  in  opposite  directions  and  at 
the  same  moment,  for  nearly  all  the  tubes  were  found  lying  in  a  heap  on  the  ground 
immediately  beneath  the  place  they  had  occupied  in  the  boiler,  the  riveting  of  their 
ends  over  the  plates  having  been  simultaneously  stripped.  The  top  of  the  furnace  and 
the  top  of  the  combustion-chamber,  which  in  the  boiler  were  immediately  beneath  the 
tubes,  had  entirely  disappeared  into  debris,  as  had  also  the  sides  and  ends  of  the  shell. 
The  boiler  seems  to  have  first  yielded  by  the  fracture  of  the  upper  row  of  horizontal 
braces.  The  loud  report  heard  when  the  pressure  attained  50  pounds  per  square  inch 
was  probably  caused  by  their  breaking.  The  larger  masses  were  all  thrown  in  one  direc- 


458  STEAM  BOILERS.  CHAP.  XIX. 

tion  at  right  angles  to  the  side  of  the  boiler,  but  the  smaller  fragments  were  projected 
radially  in  all  directions  as  from  a  centre.  Two  heavy  bomb-proofs,  constructed  of  large 
timbers  and  sand  for  the  protection  of  the  other  boilers,  were  dislodged,  and  a  part  of 
the  fence  of  the  enclosure  was  destroyed  by  the  impact  of  the  flying  fragments.  The 
crow-feet  in  most  cases  remained  firmly  attached  to  the  shell,  and  the  braces  had  parted, 
probably  in  the  welds,  leaving  the  ends  still  secured  to  the  crow-feet.  The  screw-bolts 
which  braced  the  flat  water-spaces  had  slipped  from  their  fastenings  in  the  plate  with- 
out injury  to  the  screw-threads  either  upon  them  or  in  the  plate.  The  latter  was  per- 
manently bulged  or  dished  between  the  bolts,  and  this  stretching  of  the  metal  had,  by 
its  enlargement  of  the  holes,  allowed  the  screw-ends  of  the  bolts  to  draw  out  without 
injury  to  the  threads  either  on  the  bolts  or  in  the  plates. 

"  The  ground  beneath,  and  for  a  considerable  distance  around  where  the  boiler  stood, 
was  saturated  with  the  water  of  the  boiler — in  fact,  made  into  mud — and  the  adjacent 
grass  and  small  shrubbery  were  so  drenched  that  an  ordinary  boot  was  wet  through  by 
walking  among  them.  At  seven  minutes  before  the  explosion  took  place  the  water- 
gauge  on  the  boiler  was  examined  and  found  to  indicate  the  water-level  15  inches  above 
the  top  of  the  tubes. 

"  The  conclusions  to  be  drawn  from  this  experiment  are  the  following : 

"  First.  An  old  boiler,  containing  a  large  mass  of  water  above  the  highest  point  of  its 
heating-surface,  can  be  exploded  with  such  complete  destruction  as  to  reduce  it  into 
mere  debris,  and  hurl  the  fragments  in  all  directions  with  a  force  that  no  ordinary  con- 
struction of  building  or  vessel  could  withstand. 

"Second.  That  the  pressure  required  for  so  devastating  an  explosion  is  the  very 
moderate  one  of  53f  pounds  per  square  inch. 

"  Third.  That  with  only  a  wood-fire,  generating  a  far  less  quantity  of  heat  in  equal 
time  than  a  coal-fire,  there  were  required  only  13  minutes  to  raise  the  pressure  from  the 
inspector's  working  allowance  of  30  pounds  per  square  inch  to  the  exploding  pressure  of 
53f  pounds  per  square  inch,  showing  that  a  few  minutes'  absence  or  neglect  of  the  en- 
gineer, coupled  with  an  overloaded  or  inoperative  safety-valve,  are  all  that  are  needed  to 
produce  the  most  destructive  steam-boiler  explosion,  even  with  an  old  and  unequally- 
braced  boiler,  in  which  it  might  be  supposed  a  rupture  of  the  weakest  part  would  pre- 
cede other  fracture,  and  allow  the  escape  of  the  pressure  without  doing  further  injury. 

"  Fourth.  That  in  accounting  for  either  the  fact  of  an  explosion  or  for  its  destructive 
effects  there  is  no  necessity  for  hypotheses  of  low  water,  enormous  pressures,  instan- 
taneous generations  of  immense  quantities  of  steam,  superheated  steam,  the  formation 
of  hypothetical  gases,  development  of  electricity,  etc.,  etc.  The  most  frightful  catas- 


SK.  5.  BOILER-EXPLOSIONS.  459 

trophe  can  be  produced  by  simply  gradually  accumulating  pressure  of  saturated  steam 
to  a  strain  at  which  the  strength  of  the  boiler  yields,  nor  need  that  pressure  be  much 
above  what  is  ordinarily  employed  with  boilers  of  this  type. 

"  Fifth.  That  there  is  no  flashing  of  boiler- water  into  steam  at  the  moment  of  an 
explosion.  On  the  contrary,  with  the  exception  of  the  small  portion  of  this  water 
vaporized  (after  the  reduction  of  the  pressure  owing  to  the  rupture  of  the  boiler)  by  the 
contained  heat  in  it  between  that  due  to  the  temperature  of  the  steams  of  the  explod- 
ing pressure  and  of  the  atmospheric  pressure,  it  remains  unchanged,  and  is  thrown 
around,  drenching  the  objects  near  it  and  scalding  whomever  it  falls  upon. 

"Sixth.  The  weakest  portion  of  the  boiler-braces  was  in  their  welds. 

"  Seventh.  The  equal  stretching  in  all  directions  of  the  boiler-plates  between  the 
screw-bolts,  due  to  their  bulging  under  the  pressure,  was  sufficient  to  permit  the  slipping 
out  of  the  bolts  without  injury  to  the  screw-threads  either  upon  them  or  in  the  plates. 

"Eighth.  That  this  experiment  has  conclusively  disposed  of  several  theories  of  steam- 
boiler  explosion,  replacing  vague  conjecture  and  crude  hypothesis  with  exact  experi- 
mental facts,  and,  by  thus  narrowing  the  field  for  the  search  of  truth,  has  made  the  dis- 
covery more  probable." 


INDEX. 


Acetic  acid,  Preventing  incrustation  by 441 

Acid  products  of  the  combustion  of  coal 420 

Acidity  of  water  in  boilers.  Testing  the 439 

Adamson  joint  for  furnace-flues 227 

Admiralty  Committee  on  Boilers  on  chemical  treat- 
ment of  the  feed-water  of  marine  boilers,  438, 440 

on  corrosion  due  to  fatty  acids 430,431 

on  corrosion  due  to  oxygen  and  carbonic  acid 

in  feed-waters 425 

on  corrosion  of  iron  by  chloride  of  magnesium.  426 
on  decomposition  of  chloride  of  magnesium. . .  426 
on  use  of  carbonate  of  soda  in  marine  boilers. .  440 

on  use  of  zinc  in  boilers 434 

Air,  Chemical  and  physical  properties  of 34 

Flow  of,  to  grate  of  furnace 43,  46 

Moist,  causing  corrosion 423 

Weight  of,  at  different  temperatures 45 

Weight  of,  required  for  combustion  of  fuel 40 

Weight  of,  required  for  combustion  of  various 

substances 37 

Air-admission  in  excess  of  quantity  theoretically  re- 
quired  40,  49 

through  bridge-walls 149,  324 

through  furnace-doors 327 

Algoma,  TJ.  S.  S.,  Chimney  for  boilers  of 295 

Steam-jet  for  boilers  of 300 

American   Tube-works,  Seamless  drawn  brass  and 

copper  tubes 270 

Ammonia 34 

Ammonium,  Chloride  of 440 

Angle-iron  rings,  Welding 210 

Testsof 150 

Weight  of,  per  foot  87 

Ash,  Proportion  of,  in  coals 52,  53,  54 

Specific  heat  of 41 

Ashpans 315,328 


PA6B 

Ashpit,  Dimensions  of 136 

doors,  Forms  of 327 

doors,  Begulating  the  draught  by 48 

Ashcroft  furnace-door 326 

grate 323 

spring  safety-valve 345 

Back-connection — see  Connection,  back. 

Back-draught 50,  377 

Barff  s  method  of  protecting  iron 433 

Bar-iron,  flat,  Weight  of 85 

round  and  square,  Weight  of 84 

Strength  of 83,99,100 

Testsof 103 

Baryta,  Carbonate  of 441 

Beading  the  ends  of  tubes 273 

Bearing-bars 322 

Belleville  water-tube  boiler 283 

Bending  plates 159, 164 

Bending-rolls 163 

Berryman  heater,  The 354 

Bilge-water,  Corrosive  action  of 399 

preventing  incrustation  and  corrosion 441 

Birmingham  wire-gauge 86 

Bisulphuret  of  carbon 34 

Blast-pipe,  Head  produced  by 47 

of  locomotives 299 

Bleeding- valve 350 

Blisters,  Cutting  out 404 

Formation  of 415 

Blowing  down  boilers 385 

Blowing-machines,  Work  to  be  done  by 47 

Blowing-off  causing  increased  formation  of  scale 396 

Loss  of  heat  and  water  in  consequence  of  ....  397 

Blow-off  cocks 3*5 

Blow-pipes 336 


461 


462 


INDEX. 


PAGE 

Blow-valves 335 

Boiler  of  steamer  Estelle 130,  132,  284 

of  steamer  Lookout 130,  156 

of  steamer  Lord  of  the  Isles 130,  229,  275 

of  U.  S.  S.  Daylight .127,  130,  132 

of  U.  S.  S.  Kansas 130,  132 

of  U.  S.  S.  Lackawawna 130,  142,  264 

of  U.  S.  S.  Mahaska 130,  132 

of  U.  S.  S.  Miantonomoh  and  class 130,  144 

of  U.  S.  S.  Morse 130,  132 

of  U.  S.  S.  Nipsic 130,154,  289 

of  U.S.  S.Plymouth 130 

of  U.  S.  S.  Shockokon 130,  132 

Belleville  water-tube 283 

Davey-Paxman 286 

Dickerson's  marine 129 

Double-end  cylindrical  127,  130 

Drop-flue 130,  132,  260 

Dry-bottom  226,  314 

Emery's  connected-arc  marine 124,  214 

Flue 130,  132,  260 

Herreshofl  coil 130,  132,  284 

Howard  marine  water-tube 282 

Lamb  and  Sumner 261 

Locomotive — see  Locomotive  boiler. 

Martin's  vertical  water-tube 125,  130,  263 

Perkins's  water-tube 281 

Return-flue 130,  132,  260 

Stimer's  differential  tubular 265 

Superheating 311 

Vertical  fire-tube 129 

Water-tube 280 

Boiler-building,  Systems  of 231 

Boiler-experiments 369 

Boiler-explosions — see  Explosions  of  boilers. 

Boiler-iron,  Brands  of 78 

Strength  of 78,83 

Boiler-keelsons 313 

Boiler-mountings 319 

Boiler-plates,  Dimensions  of 79 

Examination  of 105 

Forge-tests  of 102,  149 

tests  of,  English  Admiralty 104, 149 

tests  of,  French  Government 104 

tests  of,  United  States  laws  and  regulations 

regarding 92 

with  thickened  edges 199 

Boiler-power 122 

Boiling-point  of  water  at  different  pressures 71 

of  brine 395,  396 


PAGE 

Bolts  for  fastening  braces,  Strength  of 242 

wrought-iron,  Dimensions  and  weights  of 89 

wrought-iron,  Shearing  strength  of 252 

Bowling-hoop  for  furnace-flues 227 

Braces — see  Stays. 

Brass  boiler-tubes 74,  266 

Composition  and  properties  of 74,  83 

Tenacity  and  ductility  of,  at  different  tempe- 
ratures     75 

Thermal  conductivity  of 58 

tubes,  Dimensions  and  weights  of 270 

Brick,  Thermal  resistance  of 56 

Bridge- walls,  Air-admission  through 149,  324 

Calorimeter  over 136 

Fqrms  of 230,  324 

Brine,  Boiling-point  of 395,  396 

Density  of 389,  396 

Brine-pumps 335 

Bronze,  Composition  and  properties  of 74,  83 

Tenacity  and  ductility  of,  at  different  tempe- 
ratures     75 

Buckled  plates,  Stiffness  and  strength  of 117 

Butt-joints — see  Joints. 

Calcareous  deposits,  Composition  of 390 

Formation  of 391 

Thermal  resistance  of 56 

Calcium,  Chloride  of 390 

Other  salts  of — see  Lime. 

Calking 204 

Calking-tools 205 

Calorific  intensity  of  fuels 40 

power  of  coals 38,  39,  53,  54 

power  of  fuels,  Dulong's  law 38 

power  of  various  substances 37 

Calorimeter  for  measuring  actual  quantity  of  heat  in 

steam 372 

of  chimney 137,  292 

of  tubes 137,  263,  265 

over  bridge-wall —  136 

Carbon,  Chemical  equivalent  of 34 

Combustion  of 35 

Heat  developed  by  combustion  of 37 

Proportion  of,  in  different  coals 52,  53,  54 

Proportion  of,  in  iron  affecting  welding 207 

Proportion  of,  in  steel 79,  206 

Radiation  of  heat  from  incandescent  solid. ...       61 
Temperatures  of  combustion  of 41 

Carbonic  acid,  Chemical  and  physical  properties  of  . .    34 
produced  by  combustion  of  coal 35,  37 


INDEX. 


463 


Carbonic  acid  producing  corrosion  of  iron 423 

Volume  and  weight  of,  present  in  sea-water. . .  389 
Carbonic  oxide,  Chemical  and  physical  properties  of  .     34 

Combustion  of 35 

Heat  developed  by  combustion  of 37 

produced  by  combustion  of  carbon 35,  51 

Temperature  of  combustion  of 41 

Cast-iron,  Physical  and  mechanical  properties  of 83 

Tenacity  and  ductility  of,  at  different  tempe- 
ratures      76 

Thermal  conductivity  of 58 

Use  of,  in  boiler-construction 77 

Cement,  Pilling  water-bottoms  of  boilers  with 406 

Iron,  for  leaky  seams 405 

Portland,  a  substitute  for  scale 407 

used  for  boiler-beds 313 

used  for  boiler-covering 352 

Charcoal,  Calorific  power  of 38 

Combustion  of 35 

Charcoal-iron,  American 78 

Check-valves 333 

Chemical  equivalents  of  various  substances 34- 

Chimneys,  Calorimeter  of 137,  292 

Fixed 294 

Forms  and  dimensions  of 291 

Height  of 46,  47 

Hoisting 295 

Radiation  of  heat  from 46,  293 

Temperature  of 46,  47 

Chimney-draught 45,  64 

Chimney-gas,  Volume  of,  per  pound  of  fuel 42 

Weight  of  a  cubic  foot  of 45 

Chimney-stays 294 

Circular  arcs,  Stress  in 119 

Circular  flues,  Resistance  to  collapse  of 109,  229 

Circulation  of  water 59,  223 

Defective 386 

Methods  of  improving  the 387 

Cleaning  boilers 398 

fires,  Loss  of  heat  by 50 

fires,  Process  of 377 

Clinker 36 

Coal,  Calorific  power  of 38 

Character  and  efficiency  of  various  kinds  of . . . 

52,  53,  54 

Energy  developed  by  combustion  of 39 

Incombustible  matter  in 48 

Methods  of  firing  with  different  kinds  of 378 

Moisture  absorbed  by ....     49 

Rates  of  combustion  of,  in  boilers 43,  45 


Coal,  Vaporific  power  of,  in  a  boiler 39,  66 

Weight  of  air  required  for  combustion  of 40 

Coke,  Combustion  of 35,  43,  54 

Moisture  absorbed  by 49 

Combustion,  Conditions  necessary  for  perfect 40 

of  coal,  Acid  products  of  the. . .  420 

of  constituents  of  fuels 35 

of  various  substances 37 

Rates  of  42,  45,  134 

Temperatures  of 35,  40 

Volume  of  products  of 42 

Combustion-chambers  in  different  types  of  boiler 229 

Steam  generated  on  plates  of 61 

Composition — see  Brass  and  Bronze. 

Conduction  of  heat,  Laws  of 55 

Conductivity,  Thermal,  of  wrought-iron  determined 

by  Forbes 56 

of  several  metals  determined  by  B.  F.  Isher- 
wood 58 

Connections,  Back,  Arrangement  and  Construction  of  230 

Evaporation  from  surfaces  of 61 

Proportions  of 136 

Front 287 

Connection-doors 291,  327 

Convection  of  heat 55 

Copper,  Alloys  of  74,76,83 

Corrosion  of 429 

Galvanic  action  of 432 

Lining   and   coating   boiler-shells  and  tubes 

with 433 

Physical  and  mechanical  properties  of 73,  83 

Thermal  conductivity  and  resistance  of 56,  58 

tubes.  Dimensions  and  weights  of 270 

Use  of,  in  boilermaking 31,  73,  221 

Corrosion  by  galvanic  action 432 

by  oxygen  and  carbonic  acid  in  water 423 

by  sulphuric  acid  in  soot 419 

External,  of  boilers 314,  413 

Irregular  action  of,  on  iron  plates 413 

of  boilers  when  not  in  use,  Preventing  the 407 

of  steam-drums  of  U.  S.  S.  Swatara 431 

of  superheating-surfaces 310 

Corrosive  action  of  chloride  of  magnesium 425 

of  fatty  acids 427 

of  gases  of  combustion 414 

Corrosive  ingredients  of  feed-waters,  Neutralizing. . .  437 

Corrugated  flues  and  plates 221 

|  Couste  on  the  formation  of  deposits  in  boilers 

389,  391,  396 

Covering  for  boilers 351 


464 


INDEX. 


Cylindrical  shells.  Resistance  to  internal  fluid  pres- 
sure   108 

Resistance  to  external  fluid  pressure 109 

Experiments  on  collapsing  strength  of 113 

Damper 48,293 

Davey-Paxman  boiler 286 

Daylight,  U.  S.  S.,  boiler  of,  Description  of 127 

Dimensions  and  weight  of 130 

Economic  evaporation  of 132 

Dead-plate 319 

De  la  Beche  and  Playfair,  Experiments  on  efficiency 

of  coals 53 

Diagonal  lap-joints  198 

Dickerson's  marine  boiler 129 

Dissociation 41 

Drain  cocks  and  pipes 332,  351 

Draught,  Artificial 47,  298 

Efficiency  of  boilers  with 65 

Experiments  with  302 

Natural 45,  64 

of  a  furnace 43 

Drifting 171 

Drilling  boiler-plates 168 

Dry-pipes 331 

Dudgeon's  tube-expander 272,  278 

Emery,  C.  E.,  Connected-arc  marine  boiler.  .119,  124,  214 

English  Board  of  Trade  rules  for  blow-off  cocks 336 

circular  flues 229 

cylindrical  boiler-shells 218 

girder-stays 242 

safety-valves 343,  346 

stays  and  stayed  plates 239 

tests  and  inspection  of  boilers 363,  367 

English  boiler-iron,  Brands  of 79,  83 

English  Navy,  Preservation  of  boilers  in  the 407 

Specification  of  boilers  for  the 148 

Testing  boilers  in  the 363 

Tests  of  boiler-plates  in  the 102,  149 

Tests  of  steel  for  ships  and  boilers  of  the 104 

Use  of  zinc  in  boilers  of  the 43C 

Use  of  carbonate  of  soda  in  boilers  of  the 439 

Equivalent  of  heat,  Mechanical 39 

Equivalents,  Chemical 34,  35 

Erection  of  boilers 816 

Escape-pipes 347 

Estette,  boiler  of  steamer,  Description  of 284 

Dimensions  and  weights  of 130 

Performance  of 132 


Eutaw.  U.  S.  S.,  superheater  of,  Description  of 311 

Efflciencyof 68 

Evaporation  from  furnace  and  back-connection 60 

from  tube-surfaces 61,  262,  264 

Influence  of  felting  boilers  on  their  economic. .     63 

Influence  of  rate  of  combustion  on  the 66 

in  boilers  of  various  types 123,  132 

Evaporative    efficiency  of   vertical  water-tube    and 

horizontal  fire-tube  boilers 125 

Evaporative  efficiency  of  boilers,  Conditions  affecting 

the,  and  measure  of 64,  122 

Evaporative  power  of  coals 52,  53,  54 

Expanding  tube-ends 271 

Expanding-tools 272 

Expansion  of  metals  by  heat 83 

Stress  produced  by 140 

Explosion  of  boilers.  Causes  of 442 

Experimental 454 

Investigation  of 453 

Phenomena  of 450 

Theories  regarding 445 

Work  done  by 448 

of  locomotive  boilers 452 

on  the  Thunderer 451 

on  the  Westfield 453 

Eye-bars,  Experiments  on,  by  Charles  Pox 243 

by  Board  of  U.  S.  Naval  Engineers  253 

Factors  of  safety  in  boiler-construction 139,  219 

Fairbairn,  Collapsing  strength  of  cylindrical  flues. . . .  109 

Proportions  of  single-riveted  lap-joints 195 

Proportions  of  double-riveted  lap-joints 197 

Strength  of  riveted  lap-joints  190 

Fan-blowers,  Experiments  with 304 

Use  of,  for  marine  boilers 298,  300 

Work  to  be  done  by 47 

Fatty  acids,  Corrosive  action  of,  in  boilers 430 

Corrosive  action  of,  on  copper 429,  431 

Corrosive  action  of,  on  iron 428 

corrosive  action  of,  Neutralizing  the.  ..431,  439,  440 

Decomposition  of 427 

Favre  and  Silbermann,  Heat  of  combustion  of  various 

substances 36,  38 

Paying-surfaces 167 

Feed-pipes 335 

Feed-pumps 354 

Peed-valves 333 

Feed-water,  Chemical  treatment  of 437 

Grease  in 418,  430 

Introduction  of,  into  boilers 60,  334 


INDEX. 


465 


Feed- water.  Purification  of 431,  437 

Temperature  of 123,  417 

Felt,  Cowhair,  covering  for  steam  boilers 352 

Loss  of  heat  through  different  thicknesses  of. .     C2 
Felting,  Influence  of,  on  economic  evaporation  of 

boilers 63 

Ferruling  tubes  to  reduce  their  calorimeter 265 

Increase  of  holding  power  by ._ 278,  279 

Filter,  Selden's 354 

Fires,  Banking 380 

Cleaning 377 

Starting 375 

Fire-bos-iron 78,  221 

Fire-room,  Arrangement  of 122 

Air-tight 301 

Fire-tube  boiler,  horizontal,   Evaporative   efficiency 

of 66,125,262 

Vertical 129,  262,  309 

Weight  and  space  required  for 133 

Firing,  Rules  to  be  observed  in 376,  380 

Waste  of  fuel  from  careless 49 

Flame 35,  36 

Flange-iron 78 

Flanging 164 

Flat  plates,  strength  and  stiffness  of  unstayed 115 

Flat  surfaces  in  boilers 138,  238 

Floats 339 

Flow  of  air  to  grate,  Velocity  of  43,  46 

gases  in  flues,  Resistance  to 44,  46 

solids 98 

Flues,  Collapse  of 451 

collapsing  strength  of.  Experiments  on.  109, 113, 222  i 

Corrugated.      231  j 

Expansion  and  contraction  of 227,  416 

Factor  of  safety  for 140  : 

Flow  of  gases  in 44,  46 

Formulae  for  strength  of 110,  111,  229 

Laying-off  plates  for 159,  160 

Welding 208 

Flue-boilers 260  ! 

Foaming 381.  385  ( 

Forbes,  P.,  on  the  thermal  conductivity  of  wrought- 

iron 56 

Fox,  Charles,  Experiments  on  fastening  of  braces... .  243 

Fox,  S.,  Corrugated  flues  and  plates  by 221  : 

French  naval  boilers,  Capacity  of  steam-room  in 306 

Grate  bars  of 320 

Hoisting  chimneys  of 295 

Removable  tubes  in 276 

Staying  of 237,  245,  248  i 


French  naval  boilers.  Tests  of 302 

French  practice  in  proportioning  single-riveted  joints  196 
tests  for  steel  boiler-plates 104 

Friction  in  riveted  joints 173 

of  gases  in  flues 44,  43 

Fuel,  Calorific  power  and  intensity  of 38,  40 

Combustion  of 35,  40 

Elementary  constituents  of 34 

Incombustible  matter  and  moisture  in 48 

Thickness  of  bed  of,  on  grate  48,  50,  376 

Waste  of,  in  solid  and  gaseous  state 49,  51 

Furnaces,  construction  of,  General  considerations  re- 
garding  221 

Corrugated  flues  and  plates  for 221 

cylindrical,  Construction  of 226 

cylindrical,  Securing,  in  boiler 228 

cylindrical,  Strengthening-hoops  for 227 

cylindrical,  strength  of,  Rules  for 229 

Draught  of 43 

Efficiency  of 47 

Evaporation  from  plates  of 61 

in  rectangular  boilers.  Construction  of 223 

in  rectangular  boilers,  Double  tier  of 126 

in  cylindrical  boilers.  Arrangement  of 126 

Proportions  of 136 

Temperature  of 41,  60 

Furnace-crowns,  Collapse  and  repairs  of 404 

Staying  applied  to 286, 248,  251 

Furnace-doors,  Air-admission  through 327 

Construction  and  forms  of 325 

Martin's  or  Ashcroft's 326 

Prideaux's 3>6 

Fusible  plugs 339 

Galloway  tubes  260 

Galvanic  action  in  boilers 432 

Gases,  Volume  of,  &t  different  temperatures 42 

of  combustion,  Resistance  to  flow  of,  in  flues. 43,  46 

of  combustion,  Weight  of,  per  cubic  foot 45 

Gauge-glasses 337 

Gauges,  water,  Arrangement  and  forms  of 337 

water,  Indications  and  control  of 381 

Steam 340 

Georgeanna,  steamer,  Superheating  apparatus  of. ...     68 

Girder-stays 241,  250 

Glance,  IT.  S.  tug,  Furnace  of  boiler  for        225 

Grashof,  Formula  for  collapsing  strength  of  flues. . . .  112 

Grate,  Dimensions  of 136 

Form  of 319 

Indicated  horse-powers  per  square  foot  of. 123 


464 


INDEX. 


Cylindrical  shells,  Eesistance  to  internal  fluid  pres- 
sure   108 

Resistance  to  external  fluid  pressure 109 

Experiments  on  collapsing  strength  of 113 

Damper 48,293 

Davey-Paxman  boiler 286 

Daylight,  U.  S.  S.,  boiler  of.  Description  of 127 

Dimensions  and  weight  of 130 

Economic  evaporation  of 132 

Dead-plate 319 

De  la  Beche  and  Playfair,  Experiments  on  efficiency 

of  coals 53 

Diagonal  lap-joints  198 

Dickerson's  marine  boiler 129 

Dissociation 41 

Drain  cocks  and  pipes 332,  351 

Draught,  Artificial 47,  298 

Efficiency  of  boilers  with 65 

Experiments  with  302 

Natural 45,  64 

of  a  furnace 43 

Drifting 171 

Drilling  boiler-plates 168 

Dry-pipes 331 

Dudgeon's  tube-expander 272,  278 

Emery,  C.  E.,  Connected-arc  marine  boiler.  .119,  124,  214 

English  Board  of  Trade  rules  for  blow-off  cocks 336 

circular  flues 229 

cylindrical  boiler-shells 218 

girder-stays 242 

safety-valves 343,  346 

stays  and  stayed  plates 239 

tests  and  inspection  of  boilers 363,  367 

English  boiler-iron,  Brands  of 79,  83 

English  Navy,  Preservation  of  boilers  in  the 407 

Specification  of  boilers  for  the 148 

Testing  boilers  in  the 363 

Tests  of  boiler-plates  in  the 102,  149 

Tests  of  steel  for  ships  and  boilers  of  the 104 

Use  of  zinc  in  boilers  of  the 436 

Use  of  carbonate  of  soda  in  boilers  of  the 439 

Equivalent  of  heat,  Mechanical 39 

Equivalents,  Chemical 34,  35 

Erection  of  boilers 316 

Escape-pipes 347 

Estelle,  boiler  of  steamer,  Description  of 284 

Dimensions  and  weights  of 130 

Performance  of , 132 


Eutaw,  U.  S.  S.,  superheater  of,  Description  of 311 

Efficiency  of 68 

Evaporation  from  furnace  and  back-connection 60 

from  tube-surfaces 61,202,264 

Influence  of  felting  boilers  on  their  economic. .     63 

Influence  of  rate  of  combustion  on  the 66 

in  boilers  of  various  types 123,  132 

Evaporative    efficiency  of   vertical  water-tube   and 

horizontal  fire-tube  boilers 125 

Evaporative  efficiency  of  boilers,  Conditions  affecting 

the,  and  measure  of 64,  122 

Evaporative  power  of  coals 52,  53,  54 

Expanding  tube-ends 271 

Expanding-tools 272 

Expansion  of  metals  by  heat 83 

Stress  produced  by 140 

Explosion  of  boilers.  Causes  of 442 

Experimental 454 

Investigation  of 453 

Phenomena  of 450 

Theories  regarding 445 

Work  done  by 448 

of  locomotive  boilers 452 

on  the  Thunderer 451 

on  the  Westfield 453 

Eye-bars,  Experiments  on,  by  Charles  Fox 243 

by  Board  of  U.  S.  Naval  Engineers  253 

Factors  of  safety  in  boiler-construction 139,  219 

Fairbairn,  Collapsing  strength  of  cylindrical  flues. . . .  109 

Proportions  of  single-riveted  lap-joints 195 

Proportions  of  double-riveted  lap-joints 197 

Strength  of  riveted  lap-joints  190 

Fan-blowers,  Experiments  with 304 

Use  of,  for  marine  boilers 298,  300 

Work  to  be  done  by 47 

Fatty  acids,  Corrosive  action  of,  in  boilers 430 

Corrosive  action  of,  on  copper 429,  431 

Corrosive  action  of.  on  iron 428 

corrosive  action  of,  Neutralizing  the.  ..431,  439,  440 

Decomposition  of 427 

Favre  and  Silbermann,  Heat  of  combustion  of  various 

substances 36,  38 

Paying-surfaces 167 

Feed-pipes 335 

Feed-pumps 354 

Feed-valves 333 

Feed-water,  Chemical  treatment  of 437 

Grease  in 418,  430 

Introduction  of,  into  boilers 60.  334 


INDEX. 


465 


Feed-water,  Purification  of 431,437 

Temperature  of 123.  417 

Felt,  Cowhair,  covering  for  steam  boilers 352 

Loss  of  heat  through  different  thicknesses  of. .     62 
Felting,  Influence  of,  on  economic  evaporation  of 

boilers 63 

Ferruling  tubes  to  reduce  their  calorimeter 265 

Increase  of  holding  power  by 278,  279 

Filter,  Selden's 354 

Fires,  Banking 380 

Cleaning 377 

Starting 375 

Fire-box-iron 78,  221 

Fire-room,  Arrangement  of 122 

Air-tight 301 

Fire-tube  boiler,  horizontal,   Evaporative   efficiency 

of 66,125,262 

Vertical 129,  262,  309 

Weight  and  space  required  for 133 

Firing,  Rules  to  be  observed  in 376,  380 

Waste  of  fuel  from  careless 49 

Flame 35,36 

Flange-iron 78 

Flanging 164 

Flat  plates,  strength  and  stiffness  of  unstayed 115 

Flat  surfaces  in  boilers 138,  238 

Floats 339 

Flow  of  air  to  grate.  Velocity  of  43,  46 

gases  in  flues,  Resistance  to 44,  46 

solids 98 

Flues,  Collapse  of 451 

collapsing  strength  of,  Experiments  on.  109, 113, 232 

Corrugated 231 

Expansion  and  contraction  of 227,  416 

Factor  of  safety  for 140 

Flow  of  gases  in 44.  46 

Formula;  for  strength  of 110,  111,  229 

Laying-off  plates  for 159,  160 

Welding 208 

Flue-boilers 260 

Foaming 381.  385 

Forbes,  P.,  on  the  thermal  conductivity  of  wrought- 

iron 56 

Fox,  Charles,  Experiments  on  fastening  of  braces 243 

Fox,  S.,  Corrugated  flues  and  plates  by 221 

French  naval  boilers,  Capacity  of  steam-room  in 306 

Grate  bars  of 320 

Hoisting  chimneys  of 295 

Removable  tubes  in 276 

Staying  of 237,  245,  248 


French  naval  boilers,  Tests  of 362 

French  practice  in  proportioning  single-riveted  joints  196 
tests  for  steel  boiler-plates 104 

Friction  in  riveted  joints 178 

of  gases  in  flues 44,  46 

Fuel,  Calorific  power  and  intensity  of 38,  40 

Combustion  of 35,  40 

Elementary  constituents  of 34 

Incombustible  matter  and  moisture  in 48 

Thickness  of  bed  of,  on  grate  48,  50,  376 

Waste  of,  in  solid  and  gaseous  state 49,  51 

Furnaces,  construction  of,  General  considerations  re- 
garding  221 

Corrugated  flues  and  plates  for 221 

cylindrical,  Construction  of 226 

cylindrical,  Securing,  in  boiler 228 

cylindrical,  Strengthening-hoops  for 227 

cylindrical,  strength  of,  Rules  for 229 

Draught  of 43 

Efficiency  of 47 

Evaporation  from  plates  of 61 

in  rectangular  boilers.  Construction  of 223 

in  rectangular  boilers,  Double  tier  of 126 

in  cylindrical  boilers.  Arrangement  of 126 

Proportions  of 136 

Temperature  of 41,  60 

Furnace-crowns,  Collapse  and  repairs  of 404 

Staying  applied  to 236, 248,  251 

Furnace-doors,  Air-admission  through 327 

Construction  and  forms  of 325 

Martin's  or  Ashcroft's 326 

Prideaux's 826 

Fusible  plugs 339 

Galloway  tubes 260 

Galvanic  action  in  boilers 432 

Gases,  Volume  of,  it  different  temperatures 42 

of  combustion,  Resistance  to  flow  of,  in  flues. 43,  46 

of  combustion,  Weight  of,  per  cubic  foot 45 

Gauge-glasses 337 

Gauges,  water,  Arrangement  and  forms  of 337 

water,  Indications  and  control  of 381 

Steam 340 

Georgeanna,  steamer,  Superheating  apparatus  of 68 

Girder-stays 241,  250 

Glance,  IT.  S.  tug,  Furnace  of  boiler  for        225 

Grashof,  Formula  for  collapsing  strength  of  flues 112 

Grate,  Dimensions  of 136 

Form  of 319 

Indicated  horse-powers  per  square  loot  of.  ....  123 


468 


INDEX. 


Martin  furnace-door  326 

grate 833 

Miantonomoh,  U.  S.  S.,  Dimensions  and  weights  of 

boilers  of 130 

Specifications  for  boilers  of 144 

Stays  for  boilers  of 247 

Mineral  wool. 352 

Moisture  in  fuels 48 

Deterioration  of  boilers  due  to 407,  423,  427 

Morris,  Tasker  &  Co.,  Lap-welded  iron  boiler-tubes. .  269 

Morse,  U.  S.  S.,  Dimensions  and  weights  of  boilers. .  130 
Economic  evaporation  of  boilers 132 

Murphy  shaking-grate 322 

National  Tube-works  Co.,   Lap-welded  iron  boiler- 
tubes  268 

Nipsic,  U.  S.  S.,  Blow- valves  and  pipes  for 336 

Chimney  for 296 

Dimensions  and  weights  of  boilers  for 130 

Peed-valves  and  pipes  for 334,  335 

Front-head  and  tube-plate  of  boilers  for 159 

List  of  materials  for  boilers  of 154 

Smoke-connections  and  uptakes  for 289 

Stay-tubes  for  boilers  of 275 

Stop-valves  and  steam-pipes  for  boilers  of  .331,  332 
Water-gauges  for  boilers  of 338 

Nitrogen,  Chemical  and  physical  properties  of 34,  36 

Proportion  of,  in  coals 53,  54 

Oatmeal  used  for  stopping  leaks  in  boilers 406 

Oil,  Coating  interior  of  boilers  with 407 

mineral,    Preventing  corrosion  and  incrusta- 
tion by 431,  438 

vegetable  and  animal,  Decomposition  of 427 

Oil-cakes  used  to  prevent  incrustation 438 

Olefiant  gas,  Chemical  and  physical  properties  of. ...     34 

Combustion  of 35,  37 

Temperature  of  combustion  of 41 

Organic  matter  in  feed-water 441 

Overheating  of  plates,  Deterioration  caused  by 414 

Explosions  caused  by 444,  447 

Oxidation  of  iron  by  superheated  steam 412 

Admiralty  Committee  on  Boilers  on 425,  426 

Experiments  by  P.  Crau-Calvert  on 424 

Experiments  by  Scheurer-Kestner  on 424 

Oxide  of  iron,  Black 433 

Oxygen,  Chemical  and  physical  properties  of 34 

Corrosion  of  iron  by 423 

present  in  feed-water  causes  corrosion 425 

present  in  fuel,  Effect  of 36,37 


Oxygen,  present  in  various  coals 53,  54 

Volume  of,  dissolved  in  sea-water 425 

Weight  of,  required  for  combustion  of  various 
substances 37 

Painting  boilers 400 

Patching  boilers 403 

Pauksch's  boiler-tubes 276 

P6clet  on  draught  of  boilers 43 

on  transmission  of  heat 58 

Percussion,  Eifects  of,  on  strength  of  iron  and  steel.  172 

Percussion  water-gauge 389 

Perkins's  tubulous  boiler 281 

Petroleum,  Preventing  corrosion  and  incrustation  by  438 

Phosphor  in  iron  and  steel 78,  206 

Phosphor-bronze 74,  76 

Pitch  of  rivets  in  single-riveted  lap  joints. ..  188,  195,  196 

in  double-riveted  lap-joints 189,  197 

in  double- welt  butt-joints 201,  202 

Pitting 413 

Planing  boiler-plates 163 

Plate-iron,  Brands  of,  used  in  boilermaking 78 

Weight  of 84,  86 

Plymouth,  U.  S.  S.,  Chimney  of 295 

Dimensions  and  weights  of  boilers  of 130 

Superheaters  of 809 

Potash  used  for  purifying  feed- water 439 

Pressure,  External  fluid 109 

Internal  fluid 107,  108,  119 

Prideaux's  furnace-door 326 

Prosser's  expanding-tool 272,  278 

Providence  Steam-engine   Co.'s    steam-riveting    ma- 
chine    172 

Pumps,  Brine ' 335 

Feed 354 

Relative  efficiency  of  injectors  and 359 

Punch,  Forms  of 166 

Sizes  of  die  and 166 

Punched  and  drilled  rivet-work,  Strength  of 203 

Punched  holes,  Shape  of 167 

Strained  zone  around 167,  182 

Punching,  Loss  of  tenacity  due  to 167,  184 

Power  required  for 167 

Process  of 165 


Quinnebaug,  U.  S.  S.,  Chimney  for 298 

Radiation  of  heat  from  felt-covered  boilers  and  pipes.  62 

from  boilers  and  pipes,  Means  of  preventing.. .  351 

from  incandescent  carbon 61 

Laws  of 55 


INDEX. 


469 


PAGK   1 

Rankine,  W.  J.  M.,  Formula  for  efficiency  of  boilers.    65  I 

Formula  for  efficiency  of  heating-surfaces 59 

Rule  for  area  of  safety-valves 343 

Repairing  boilers 403 

Reverse- valve 351 

Rivets,  corroded,  Specimens  of 417 

Crushing  action  between  plates  and 185, 186 

Dimensions  of 187,  195,  203 

Formsof 176 

Leaky 402 

Oval  199 

Pitch  of 188, 189,  301 

Shearing  strength  of 184,  192 

Steel 81,  176 

Testing 103 

Weights  of 91 

Rivet-holes,  Countersunk 177 

Half-blind 171 

Laying  off 158 

Punching  and  drilling 167,  168 

Rivet-iron 83 

Rivet-points,  Forms  of 176 

Length  of  shank  required  for 177 

Riveted  joints — see  Joints,  riveted. 

Riveting,  Chain  and  zigzag 178,  189 

Cold 175 

countersunk,  Strength  of 191 

Hand  and  machine 171,  173,  175 

over  tube-ends 273,  278,  279 

Riveting-machines,  Steam  and  hydraulic 172,  173 

Rodman  testing-machine 93 

Saddles  for  cylindrical  boilers 315 

for  dry-bottom  boilers 314 

Safety,  Factors  of 139,  219 

Safety-valves,  Area  of 342,  343 

Arrangement  and  forms  of 341,  343 

Construction  of,  in  accordance  with  regulations 
of  supervising  inspectors  of  steam-vessels. . . .  344 

Derangement  of 443 

Effective  opening  of 342 

lever,  Formulae  relating  to 346 

lever,  Practical  method  of  loading 347 

spring,  Rules  of  Board  of  Trade  (English)  for.  346 

Sal-ammoniac 440 

Saline  matter  of  sea-water.  Constituents  of 388 

Salinometer,  Description  of  the 393 

Graduating  the  394 

pots 340 

Salt,  common,  Weight  of,  contained  in  sea-water. . . .  389 


Saponaceous  deposits  in  land  boilers 418 

Saturation  of  water  in  boilers,  Testing  the 393 

with  regard  to  sulphate  of  lime 395 

Scale  in  boilers,  Composition  of 390 

Formation  of 391 

Preventing  the  formation  of 393,  435,  437 

Protection  against  corrosion  by 406 

Scaling  boilers 400 

Screw-stays 243 

Experiments  on 255 

Sea-water,  Density  of 388 

Distilled 423,  435 

Salts  contained  in 389 

Specific  heat  of 395 

Volumes  of  gases  dissolved  in 425 

Sectional  boilers 280 

Selkirk's  tube-beader 273 

Sellers  &  Co.,  Wm.,  Portable  riveters  by 174 

Self-adjusting  injectors  by 359 

Size  of  die  in  punching-machines  of 166 

Setting  boilers 313 

Shaw's  spiral  nozzles 350 

Shearing  boiler-plates 163 

Shearing  strength  of  bolts  and  pins  in  braces 242 

of  rivets 184,  193 

of  wrought  and  cast  iron 83 

of  wrought-iron  bolts,  Experiments  on 252 

Shell  of  boilers,  cylindrical,  Arrangement  of  tubes 

and  furnaces  in 126 

cylindrical,  Building  and  constructing. 170,  216  231 

cylindrical,  Laying  off  plates  for 159,  160,  161 

cylindrical,  Rules  for  strength  of 217 

cylindrical,  Rupture  at  longitudinal  seams. . . .  453 
cylindrical,  Strains  caused  by  differences  of 

temperature 417 

cylindrical,  Weakened  by  steam-domes. 308 

cylindrical,  Weakened  by  manholes 329 

cylindrical,  Welding  the  seams  of 209 

Formsof 123,214 

Quality  of  iron  for 78,  215 

Rectangular  123,  126,  215 

Shell-iron 78,  215 

Shock,    W.   H.,  Experiments  on  holding  power  of 

boiler-tubes 277 

Experiments  on  influence  of  hammering  on 

tenacity  and  ductility  of  wrought-iron  bars.  100 
Experiments  on  shearing  wrought-iron  bolts. .  252 
Shoekokon,  IT.   S.    S.,   Dimensions  and   weights  of 

boilers  of 130 

Economic  evaporation  of  boilers  of 132 


470 


INDEX. 


Silicon  in  iron 78,  206 

Smoke,  Formation  of 36 

Losses  due  to  formation  of 51 

Smoke-connections — see  Connections,  front. 

Smoke-pipe — see  Chimney. 

Socket-bolts 243 

Leaky 403 

Soda,  Arseniate,    hyposulphite,  oxalate,  and  phos- 
phate of 440 

Sulphate  of 439 

Tannate  of 441 

Use  of,  for  preventing  corrosion  of  boilers. . .  .  407 
Use  of,  for  purifying  feed-water 439 

Sodium,  Chloride  of,  in  sea-water 389,  890,  391 

Soot,  Formation  and  character  of 36,  420 

Sulphuric  acid  in  419 

Specific  gravity  of  coals 52,  53,  54 

Specific  heat — see  Heat,  specific. 

Specifications  of  boilers 141 

for  boilers  of  the  English  navy 148 

for  boilers  of  U.  S.  S.  Lackawanna 142 

for  boilers  of  U.  S.  S.  Miantonomoh 144 

Spherical  forms  in  boiler-construction 138 

shell,   Resistance  of,   to  internal  fluid   pres- 
sure    107 

Spheroidal  condition  of  water 415,  446 

Stay-bolts,  Experiments  on  screw 255 

Forms  and  dimensions  of 243,  259 

Leaky 403 

Stay-domes  252 

Stayed  plates,  Experiments  on  strength  of 255,  258 

Formulas  and  rules  for  strength  of 238,  239,  258 

Strains  in,  caused  by  differences  of  tempera- 
ture   418 

Staying,  Methods  of 234 

Stay-plates  , 251 

Stays,  Corrosion  of 238 

Experiments  to  determine  proportions  of  pins, 

eyes,  and  shanks  of 253 

Factor  of  safety  for 141,  238 

Fastenings  of 242,  247,  249 

Fitting  and  adjusting 249 

for  chimneys 294 

Girder 241,  250 

Gusset 241,  S51 

Proportioning 237 

Rupture  of 451 

Strains  on 117,119,237 

Various  forms  of 245 

Stay-tubes 274 


Steam  decomposed  by  heat 446 

Dry 67 

Properties  of 71 

superheated,  Boiler  explosions  ascribed  to 447 

superheated,  Density  of 67 

superheated,  Dynamic  efficiency  of 67 

superheated,  Isherwood's  experiments  with..  . .     68 

superheated,  Oxidation  of  iron  by 412 

Weight    of,    discharged  from   an   orifice    per 

second 342 

Steam-drums,  Arrangement  and  forms  of 307 

Corrosion  of 431 

Laying  off  plates  for 162 

Weakening  of  cylindrical  boiler-shells  by 308 

Steam-jet,  Efficiency  of 300 

Experiments  with 302 

Forms  and  arrangement  of 300 

Koerting's 301 

Steam-pipes 332 

Steam-room,  Capacity  of 306 

Height  of 307 

in  different  boilers  130 

Insufficient 306 

Steam  stop-valves 331 

Steel  bars,  Appearance  of  fracture  of 101 

boilerplates,  Experiments  en  strength  of  riv- 
eted joints  of 193,  204 

boiler-plates.  Tenacity  of 80,  82,  83 

Corrosion  of 80,  413 

Physical  and  mechanical  properties  of 83 

plates,  Annealing 81,  167,  416 

plates,  Power  required  to  punch 167 

plates,  Weightof 86 

plates,  Welding 206 

rivets , 81,83,  176 

Tenacity  and  ductility  of,  at  various  tempera- 
tures  76,  415 

Tests  of 82,  104 

tubes 267 

Use  of,  in  boiler-construction 79,  80,  81 

Stimer's  differential  tubular  boiler 265 

Stop-valves 331 

Strains  due  to  variations  and  differences  of  tempera- 
ture   416 

in  riveted  joints 180,  191 

Strength,  Apparent,  of  riveted  plates 180,  192 

Apparent,  of  test-specimens 96 

of  iron  and  steel,  Effect  of  percussion  on 172 

of  materials  in  riveted  joints 183 

of  various  metals 83 


INDEX. 


471 


PAOE    | 

Strength  of  wrought-iron  bars,  Effect  of  rolling  and 

hammering  on , 98 

Shearing,  of  wrought-iron  bolts 253 

Strengthening-hoops  for  furnace-flues 227 

Strengthening  plates  and  rings  around  manholes 329 

Stress,  Effects  produced  by 97 

Stub's  wire-gauge 271 

Sulphates   of    lime    and    magnesia — see    Lime   and 
Magnesia. 

Sulphur,  Chemical  and  physical  properties  of 34 

in  fuel 36,  53,  54 

in  iron 77 

Sulphuretted  hydrogen,  Properties  of 34 

Sulphurous  acid,  Chemical  and  physical  properties  of.     34 

Sulphuric  acid  in  soot 419 

Superheated  steam — see  Steam,  superheated. 

Superheated  water  in  boilers. ...  447 

Superheaters,  Arrangement  and  forms  of 68,  309 

Corrosion  of 310 

Efficiency  of 69,  310 

Lloyd's  rule  for  cylindrical  shell  of 218 

Superheating,  Methods  of 69 

Superheating  boilers  of  United  States  naval  vessels. .  311 

Superheating  steam-pipes 333 

Supervising  inspectors  of  steam-vessels,  Rules  of,  con- 
cerning fusible  plugs 339 

concerning  hydraulic  tests  of  boilers 364 

concerning  safety-valves 343,  344 

concerning  temperature  of  feed- water 417 

concerning  tests  of  boiler-plates 92 

concerning  water-gauges 337 

Swaging  tubes  265 

Swafara,  U.  S.  S.,  Corrosion  of  steam-drums 431 

Sweating  of  boilers 427 

Tallow,  Decomposition  of 428,  429,  431 

Use  of,  in  boilers 386,  408 

Tannate  of  soda 441 

Tannic  acid 440 

Temperature,  Differences  of,  in  a  steam  boiler 60,  417 

differences  and  variations  of,  Strains  produced 

by 140,  416 

Influence  of,  on  tenacity  of  metals 75,  415 

Influence  of.  on  limit  of  saturation 395 

of  chimney  of  marine  boilers 47,  66 

of  combustion  of  various  substances 40 

of  feed-water 123,  417 

of  furnace  in  marine  boilers. . . 41,  60 

of  gases  in  tubes  of  boilers,  Differences  of.   .  .       62 
of  gases  in  uptake,  Method  of  determining 372 


Temperature  of  ignition 35 

of  steam  at  different  pressures 71 

Testing-machine,  Rodman's 93 

Tests  of  boiler-plates  for  English  naval  vessels 149 

of  boiler-plates,  Forge 102 

of  boiler-plates,    U.  S.   laws  and  regulations 

about  92 

of  boilers  by  expansion  of  water 366 

of  boilers,  by  steam 366 

of  boilers,  Hammer 369 

of  boilers,  Hydraulic   363 

of  boilers,  Laws  and  regulations  regarding. . . .  362 

of  steel  for  boilefs 82,  104 

Test-specimens,  Form  and  dimensions  of 96 

Thermal  conductivity,  Formulae  for 56 

of  wrought-iron,  Forbes  on 56 

of  various  metals,  Isherwcod  on 58 

Thermal  resistance  of  various  metals 66 

of  plates  and  tubes  in  a  boiler 59 

Thermal  unit,  British 37 

Thermometers  341 

Thurston,  R.  H.,  Formula  for  area  of  safety-valves. .  343 

Work  done  in  exploding  a  boiler 448 

Tin,  Alloys  of  copper  and 74,  83 

Proto-chloride  of 440 

T-iron  rings  for  furnace-flues 227 

Tests  of 151 

used  for  staying  and  stiffening  boiler-plates.  236, 251 

Weight  of 88 

Trenton,  U.  S.  S. ,  Smoke-connections  and  uptakes  of  290 

Tube-beader,  Selkirk's 273 

Tube-brushes 398 

Tube-expanders 272 

Tube-scrapers 398 

Tube-sheets,  Bulged 405 

Drilling  holes  in 271 

Laying  off,  for  boilers  of  U.  S.  S.  Nipsic 159 

Raymond's  recessed 272 

Stay-rods  for 274,  276 

Tubes,  Arrangement  of,  in  marine  boilers 125,  262 

Brass 74,  266 

Calorimeter  of 137,  263 

Collapse  of 451 

conical,  Laying  off  plates  for 160 

Copper 266 

Dimensions  and  spacing  of 138,  262 

Drawn  seamless 267 

Evaporation  from  61,  263,  264 

Expanding  271 

Ferruling  and  swaging 265,  278 


472 


INDEX. 


Tubes,  Fire 264 

fitting,  Bad  workmanship  in 368 

Galloway 260 

Hanging 286 

Lap- welded  iron 266,  268 

Leaky 383,  405 

Pauksch 276 

Plugging  leaky 383 

Kemovable 276 

Scaling 401 

Secured  by  various  methods,  Holding  power  of  277 

Stay 274 

Steel .- 267,  268 

Sweeping 398 

Water 263,  266 

Tweddell's  hydraulic  machine-tools 173 

hydraulic  tube-expander. 273 

Uptakes,  Arrangement  of  287 

must  be  air-tight  291 

of  cylindrical  boilers 289 

of  rectangular  boilers 288 

Securing  chimney  to 294 

U.  S.  laws  regarding  factor  of  safety  in  marine  boilers  140 

regarding  inspection  of  marine  boilers 366 

regarding  tests  of  boiler-plates 92 

regarding  tests  of  marine  boilers 362 

U.  S.  naval  boilers,  Ashpit-doors  of 328 

Blow-valves  of 335 

Chimneys  of 295,  296,  298 

Connection-doors  of 327 

Furnace-doors  of 325 

Grate-bars  of 320 

Hydrometer  used  for 393 

Manhole-covers  for 330 

Rectangular 215,  223,  225 

Regulations  for  care  and  preservation  of 408 

Removable  tubes  used  in 277 

Saddles  for 314,  315 

Salinometer-pots  of 340 

Specifications  for 142, 144 

Superheaters  of 309,  311 

Tests  of 362 

Water-gauges  for 338 

Vacuum-valve 351 

Vapor,  aqueous,  Chemical  and  physical  properties  of    34 

Vaporific  power  of  coals 39,  52,  53,  54 

of  dry  pine-wood 52 

of  various  substances 37 


Ventilators,  Fire-room,  of  U.  S.  S.  Miantonamoh 148 

Volume  of  air 34,  42 

of  gases  at  different  temperatures 42 

of  steam  at  different  pressures 71 

of  various  gases 34 

Washers,  Standard  sizes  and  weight  of 90 

Water,  Circulation  of,  in  boilers 59,  223,  386 

decomposed  by  heat  alone 446 

Distilled  sea 423,  425 

of  different  seas,  Analysis  and  density  of 388 

present  in  fuels 36 

Chemical  and  physical  properties  of 34,  71 

Spheroidal  condition  of 446 

Superheated 447 

Water-bottom  of  boilers 225 

Filling,  with  cement 406 

Water-bridge 230 

Water-gauges 337,  381 

Water-gauge  glasses 337 

Water-legs 226 

Water-level 138 

Water-room  in  boilers 306 

Water-saponification 427 

Water-spaces  in  boilers 137 

Water-tubes,  Horizontal 280 

Vertical 125,  263,  266 

Weight  of  atmospheric  air  per  cubic  foot 34,  45 

of  atmospheric  air  and  oxygen  required  for  com- 
bustion  37,  40 

of  boilers  of  a  given  power 133 

of  boilers  of  various  types 130 

of  chimney-gas  per  cubic  foot 45 

of  drawn  brass  and  copper  tubes 270 

of  flat  bar-iron  per  foot 85 

of  lap- welded  iron  boiler- tubes 268,  269 

of  rivets 91 

of  sheet  and  plate  iron 86 

of  steam 71 

of  steel  plates 86 

of  various  gases  per  cubic  foot 34 

of  various  metals  per  cubic  foot 83 

of  wrought  angle-iron 87 

of  wrought-iron  bolts 89 

of  wrought-iron  plates  and  bars 84 

of  wrought  T-iron  88 

Welded  joints,  Strength  of 211 

Styles  of. 208 

Welding,  Theories  and  instructions  regarding 206,  210 

angle-iron  rings 210 


INDEX. 


473 


Welding  boiler-plates 207 

cylindrical  boiler-shells 809 

front  plates  of  boilers 210 

furnace-flues 208 

Weslfield,  steamer,  Boiler-explosion  on  453 

Wire-gauge,  Birmingham 86 

Stub's 271 

Wood,  Calorific  power  of 37,  52 

Moisture  in 49 

Workmanship,  Examples  of  bad 367 

Rules  of  Board  of  Trade  (English)  regarding. .  218 

Wrought-iron,  Appearance  of  fractures  of 101 

Corrosion  of 31 

Ductility  of 83, 100 

Ductility  and  tenacity  affected  by  hammering 
and  rolling 98 


Wrought-iron,   Ductility  and  tenacity  at   different 

temperatures 76,  415 

Physical  and  mechanical  properties  of 83 

Thermal  conductivity  of 56,  58 

used  in  boiler-construction 31,  77 

Wyoming,  U.  S.  S.,  Experiments  with  boilers  of 266 


Tcmtie,  U.  S.  S.,  Supports  for  boilers  of 315 


Zinc,  Alloys  of  copper  and 74,  83 

Corrosion  and  incrustation  prevented  by 434 

Instructions  regarding  its  use  in  English  naval 

boilers 436 

Thermal  resistance  of 55 


OF  THE 

UNIVERSITY 

OF 


Plate  L 


1 

=n 

--               «2 

-i-^n-r--!!  —  "-^i^-. 

r> 

"i 

i       .ni 

-1—  t^Vn                   V 

n     ij.  : 

-^n 

:& 

Hfi 
^g 

^pO;La33l-T^>l 

-^    '     oa      ^ 

n 
<> 

1  ^J                      HH        • 

JLX-l  

OF   THE 

UNIVERSITY 

OF 


Experiments  on  Tens 
Conducted  at  tfu 

CMefEngit 


Bl.      1          B2.               B3.               Bl.      1  //• 

•< 

11 

! 

<i 

e4 

4 

Jl 

— 

tl 

<! 

rf 

«! 

r 

1 

-; 
<! 

••* 

•« 

( 
—  N 

5 

- 

«5 
•4 

•  i 

i 

«5 
•< 

;c 

^ 

1 

<i 
< 

fill    I 

Bl.                 B2.                 B3.                 Bt. 

69° 


C3. 


C3. 


0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.625 

0.648 

0.629 

0.620 

0.634 

0.778 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.307 

0.330 

0.311 

0.302 

0.316 

0.475 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

0.500 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

4.285 

4.284 

4.275 

4.302 

4.250 

4.190 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

0.410 

0.409 

0.400 

0.427 

0.375 

0.315 

27100 

27000 

26500 

26600 

26450 

28050 

10000 

20450 

14000 

18000 

10250 

16850 

13175 

54200 

540OO 

53000 

53200 

52900 

56100 

20000 

40900 

28000 

36000 

20500 

33700 

26350 

^                   rk-ft>^>)ta'                ^/ 

V.             r»o  -f  ty  ff 

Jot/OO 

ai%ff5 

rfU-L'J  i  .O 

hngth  of  Wrought  Iron, 
mngton  Navy  Yard, 

•: 

**'.  Shock  U.  S.  JV. 


Plate  II. 


'    <.'-.                C3.                C4. 

S 

* 

T> 

-f 

•pi 

rt 

0 

SKETCH 
OF 
SPECIMENS 
BEFORE 
TESTING. 

•  1     "l  

(   }  1 

1  —  IVi 

rfi  —  ir 

y. 

i       rf 

RlRfl 

f-S 

V             —  ' 

S       S 

5 

Q      ( 

!l 

2 

il! 

il  —  i 

n      J 

n 

•> 

r~  —  \  ^~ 

'  -. 

\}  ' 
C3.                C4. 

1 

"-N  .^-             --S 

—  U-j 

ri 

H 

3    § 

rf 

J-T 

J^ 

-  v 

iQI 

B     © 

i  —  M 

so 

H 

___ 

w 

" 
I 

n 

H 

__1 
X 

o    o  1 

Ji^ 

Q 

5 

Is  h 

N 

TV     -i 

LJ^r 
11 

U 
_J~T 

|  — 

r 

0 

74° 
D2. 

71° 

D3, 

\  ( 

ii 

63° 

63*                    63"'                     63 

ft 

63° 
E6. 

1 

E6. 

-^^—  ^^— 

6S° 
E7. 

E7. 

6S° 

SKETCH 
OF 
SPECIMENS 
AFTER 
TESTING. 

J  1  D1- 

E3. 

E4.                    E5. 

1             E8. 

E3. 

K 

I 

i 

E.*. 

II 

H  W 

1 

-i    |       Dl. 

m 

D3. 

r 

El. 

E2. 

E4. 

0.798 

0.798 

0.798 

•>    0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

0.798 

O.798 

DIAMETER 
BEFORE  TESTING. 

0.775 

0.7  5  O 

0.770 

0.745 

0.650 

0.640 

0.635 

0.616 

0.643 

0.625 

0.627 

0.625 

DIAMETER 
AFTER  TESTING. 

0.500 

0.500 

0.500 

0.500 

0.000 

0.500 

0.500 

0.500 

0.500 

0300 

0.000 

0300 

AREA  OF  SECTION 
BEFORE  TESTING. 

0.472 

0.442 

0.466 

0.436 

0.332 

0.322 

0.317 

0.298 

0.325 

0.307 

0.309 

0.307 

i  AREA  OF  SECTION 
AFTER  TESTING. 

3.875 

3.875 

3.875 

3.875 

3 

.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

3.875 

LENGTH 
BEFORE  TESTING. 

4.175 

4.265 

4.205 

4.265 

4 

.200 

4.29O 

4.290 

4.290 

4.300 

4.290 

4.265 

4.349 

LENGTH 
AFTER  TESTING. 

0.300 

0.390 

0.330 

'    0.39O 

0.325 

0.415 

0.415 

0.415 

0.425 

O.415 

0.390 

0.474 

ELONGATION. 

2Z75t 

»  25300 

25300  25700 

262OO 

26200 

26000  25900 

2650O  25700 

25950  26000 

ABSOLUTE 
BREAKING  STRAIN 

S150i 

)  50600 

£0601 

)  5^00 

524OO 

52400 

52000  51800  53000  51400 

51900  5200C 

>       BREAKING  STRAIN 
PER  SQUARE  INCH. 

!~rt  -• 

12.5 

/  AVER.  BREAK,  STRAIN 
PER  SQUARE  INCH. 

&JAJ4&    - 

O<i  J- 

MJttCLL  A  arRUTHERS,   EHG'S,  M.Y. 

Kg.  1. 


Plate  III. 


BOILER  FOR  U.  S.  S."  DAYLIGHT." 


9— - 


/OOOOOOOOOO  ; OOOOOiOO OOO    O0OOOOOOO' 

poooooooooJpooootaoooo  Sboooooooi 

OOOOOOOOOO  |OOOOOJOO OOO    OOOOOOOOOOi 

oooooooooo ! oooooooooo  oooooooooo 
loop  oo  oo  ooo  iooooo'oo  ooo  ooo  oo  oo  ooo] 

o 


TO 


15- 


,15" 

i—  -8 

3" 

* 

IjL     \f                                                                    >. 

\ 

T 
i 

i 

i 

\ 

| 

i 
i 
J 

I] 

i 

| 

' 
. 

00 

-2-0 

,1    I 

i 

'I1 

i 

•f^T 

CD 

6'-3-  -                -•  -19-  ^ 

-OD 
'^                 **  tj'         "     '  " 

f 

i 

!T 

-6-8 

e-< 

d 

i 

•  i 

"s 

i 

~;™r- 

^  9'll"      ''  

Kg.  2. 

TWO  BOILERS  FOR  U.  S.  S.  "  KANSAS.' 


!^7-'37UF-": 


;  O :  :•  O  •'.' '.':  O  O  O  O  O  O  O  O  :h '.';  O  O  O  O  O  O  O  O  O  O  O  G 
i  O  Oii  C-O-Q.O  O  O  O  O  '.'i 


8  -  ii-          "l; 

°     ^/^/^  /-w\  /^i? 


oooo;oooc 

OOOQ-OOOC 

oooqpoo 


OGOCTOOCK 
OOOOIOOOC 
-..-.„  OOOO.OO  OC  „ 

jjooooooivo  \Sp_oop  bop/  o 

'o 


;'.VOOOOOOOO 

coooooooo 


'- 


-—3'- 4"-— 


? 


-6^-10'-, 


ig.  3. 

TWO  BOILERS  FOR  U.  S.  S.  "  MAHASKA." 


— , 6—10- IO-38? 


Plates  IY.  &  V. 


1 

1 

1 

1 

•  •< 

to. 

s 

**  • 

• 

o 
o 

z 


H 
O 

z 

•n 
3D 

m 

O 

Z 
-I 

O 
O 

o 

2 
o 

< 

m 


-o 

> 

(0 

CO 


O 


O 
O 
O 

2 
O 

< 
m 


Plate  VI. 

BOILER  FOR  U.  S.  S.  "LACKAWAh 


CI112«0          1  2  3  4  5  6 

Scale:  N^H- 1-—     !        I \ h= — t i  1 


11-9- ^ 


-7-10- 


rf 


0 


r 


Of  THE 

UNIVERSITY 

Of 


o 


o 


o 


o 


o 


o 


BOILER  FOR  U.  S.  S.  "LACKAWAN 


\ 


Scale: 


12     6     0  1  2  3 


Section  A,- B. 


Plate  YH. 


OOOOOOO 
OOOOOOO 
OOOOOOO 
OOOOOOO 
6  OOOOO  O 
OOOOOOO 
OOOOOOO 
OOOOOOO 
OOOOOOO 
OOOOOOO 
OOOOOOO 
OOOOOOO 

oooooo  o 

OOOOOOO 

8 ooooo  o 
oooooo 

OOOOOOO 

§00000  o 
oooooo 
ooooo  o 

OOOOOOO 
OOOOOOO 
OOOOOO  O 
O  OOOOO  O 

oooooo 
oooogo. 


§00000000  o 
OCOQ  O OOOO 
ooooooooo 
oooooooooo 

8  OOOOOOOOO 
ooooooooo 
oooooooooo 
oooooooooo 
ooooooooco 

OOOOOOOGOO 

oooooooooo 

OOOOOOOOOO 

oooooooooo 
oooooooooo 
oooooooooo 

" OOOOOOOO 

oooooooo 
oooooooo 

"OOOOOO 

oooooo 
oooooo 

~  OOOO 

oo 
o 


•; 


oo 

8 

oOcoo" - 
ooooo  _  _ 

OOOOOQO 

°OOOQ88888 
8888 

gQQQ 

_ooo5oo66 , 

OOOOOQOOOO 

ooooooooo ~ 


00_ 

..88888 

ooooooooo 

OQ  OOOOOOO 

oooooocoo 

uOOOOOOOOO 

o ooooooooo 
oooooooooo 

8  OOOOOOOO 
oooooooo 

. 


6 


o 

OOOO 

ooooo_ 
ooooooOoo 

OQOOOOOOQ- 

oooooooooo 

OOOOOOOOOO 

ooooooooc 
oooooooooo 
9QQ5QOQQQQ 


• 
ooooo 

80  o  o  o 
o  oo  o 
00  ooo 
ooooo 

ooooo 
ooooo 

oo5o 


,  oo 

OOOOOOO 

-  OOOOOOO 

oooooooo 

_  OOOOOOO  O 
OOOOQOOOOO 

oooooooooo 
oo 


ooo 


oo 


OOOOOOOOO 

ooooooooo 
oooooooooo 
ooo  oc  ooooo 

OOOOOOOOOO 
rS  ^O  O  O  QD  O  O 


ooooc 
o  oooc 
ooooc 

8  ooooc 
ooooc , 
ooooooc 

8  oooc 
oooc 
ooooc 

ooooc 

oooooooc 

OOOOOOC  ' 

ooooooc 

oooooooooc 
ooooooooc 
ooooooc - 
ooooooc . 
o  o  go  o  o  Q.C 


Section  E.  -  F. 


1 

\ 

1    \ 

:|        i          1           1.         i        \ 

i 

Section  C.-D. 


-•:  _ 


SIX  BOILERS  FOR  U.  S.  S. 

BUREAU  OP  STEAM  ENGINEE 


Scale: 


12 


© 


•>> 


f  6600660001 
ooooooooo1 

f    OOOOOOOOO! 
fOOOOOOOOOO; 

M|oboooooooo| 

lopqgopogogi 

^TOQQ^OT^ 

I^^H"'   ~-i*L~: 


111' 


OOOO 
OOOO 
OOOO 
OOOO 


OOOO 


o 
o 
o 
o 
o 
o 
o 


o 
o 
o 
o 
o 
o 


o 


o 


o 
o 
o 
o 
o 
o 
o 


o 
o 
o 
o 
o 
o 


o 


o 
o 
o 
o 
o 
o 


o 
o 
o 
o 
o 
o 


o 
o 
o 
o 


o 
o 

\ 

o 
o 


o 


o 


o 
o 


)  O  O  OOOOO  OOOOO  OOOOO  OOOOO  OO  6% 
)OO  OOOOO  OOOOO  OOOOO  OOOOO  OOOOL 
)OO  OOOOO  OOOOO  OOOOO  OOOOO  OOOO'; 
)OO  OOOOO  OOOOO  OOOOO  OOOOO  OOOO 


o 


o 


o 


o 


o 


o 


OOOOOOOOOOOOOOOOO  OOOOO  O'O  O  C 

' 


/Q: 


vQ\ 


/Jtl 


-7J'-- 


(o  o  g  o  o  o  o ' 
\o/ 


OO 


o 


o 


ooo< 
o 


0 


o    o 
ID    o     o 


\o\ 


o// 


•of 


_QO< 


8 


--10- 


QO  o> 


fo/ 


\O; 


IANTONOMOH  &  CLASS. 

EC&,  U.  S.  NAVY  DEPABTMEJTT. 


=Feet. 


Plate 


BRACING  OF  BOILERS 

FOR  U.  S.  S.  MIANTONOMOH  &  CLASS. 


Plate  IX. 


Scale 


0 a 6 9  12  15  18  21 


U.S.S."AMPHITRITE:' 


U.S.S,   MONADNOCKV 


<TT)FOK  FRONT  A  BACK  HEADS. 


FOR  BACK  CONNECTION. 

I « 


U.S.S."TERROR." 


=i \ 


FOR  FRONT  &  BACK  HEADS 


» U.S.S."MIANTONOMOH 


Plate  X. 


GO 
•n 
O 
37 
0) 
O 

r- 
m 
73 


H 
m 


O 
O 
?«; 
O 

c 

H 


H 
m 

(O 

•n 
O 

73 
00 
O 


37 
CO 


CO 

• 

CO 


•o 

CO 


If  \ 

' 


JA^JTO 


OOOOOOOO 1 

ooooooooo^ 
ooooooooo  ^ 
oooooooooo 
oooooooo 
oooooo 

OOOOQ 


BOILER    FOR    STEAMER 

BUREAU    OF    STEAM-ENGINEERING, 

Grate-surface, 

Heating-surface,  ..... 

Calorimeter  of  tubes,  .         .  .         . 

Ratio  of  calorimeter  to  grate-surface,   . 
Ratio  of  grate  to  heating-surface, 
Capacity  of  steam-room,      . 

Weight  of  boiler, 

Weight  of  water  (to  \\  inches  above  tubes), 


TUBES. 


Number, 

Outside  diameter, 
Thickness,    . 
Total  length, 


.<:OKOUT." 


Plate  XL 


1878. 


23.00  sq.  ft. 
.  518.97  sq.  ft. 
.       3.14  sq.  ft. 
i  to  7.32 
i  to  22.56 
.    94.5  4  cub.  ft. 
20,910  Ibs. 
8,740  Ibs. 


.     114 

2-j-  inches. 
.  No.  t2\V.  G. 
.  6  feet  2|  ins. 


SIX    BOILERS    FOR    U.    S.    S.    "NIPSIC." 

BUREAU     OF     STEAM-ENGINEERING,     JUNE,     1877. 

The  boilers  are  to  be  constructed  of  the  best  American  charcoal  flange-iron.  All  seams  not  in  contact  with  th 
fire  to  be  double-riveted.  All  the  plates  to  be  planed  on  the  edges,  the  seams  to  be  butt-jointed  (planed)  and  covere 
with  double  longitudinal  straps  on  the  shell,  £  inch  thick  ;  the  straps  on  the  heads  to  be  single,  £  inch  thick  ;  all  t 
be  double-riveted  and  calked  perfectly  tight.  Gussets  and  stay-plates  to  be  made  of  the  best  flange-iron,  eac 
riveted  to  the  shell  and  heads  by  a  flange  2^  inches  wide,  and  an  angle-iron  2^  X  2-J-  inches  ;  the  grain  of  the  iron  to  b 
placed  in  the  direction  of  the  strain  on  the  stay-rods.  Stay-domes  a,  b,  c  to  be  made  of  the  best  flange-iron,  \  inc 
thick.  All  plates  used  in  the  construction  of  these  boilers  to  stand  a  test  not  less  than  55,000  pounds  per  square  inch 

The  sections  of  the  furnaces  are  to  be  riveted  together  so  as  to  bring  all  the  welded  seams  in  line  with  eac 
other.  Special  care  must  be  taken  to  have  the  welded  seams  of  the  furnaces  come  below  the  grate-bars,  about  on  th 
lines  marked  d  d. 

The  inner  row  of  rivets  around  manhole  to  be  countersunk,  flush  on  the  inside.  Tubes  to  be  of  drawn  bras! 
and  to  be  expanded  by  the  Prosser  tool. 


Scale: 


12 


JL 


Feet. 


o  o  o  Q-o  o  o  o  o  o  o  o 
ob  oe  CK>O  o  o  o  o  o  o 
booooooooooo 

O  O  O  Q,£>  OOOOOOOO 
O  O  O  O  D  O  O  O  O  O  O  O  O 
":00O  OOOOOOOO 

^oooooooooo 


THICKNESS   OF    PLATES. 

Shell  and  circular  butt-straps, 
Heads  and  back-connections, 

Tube-sheets,  

Furnaces,         •         .        .         .     ,  .        . 
Gussets  and  angle-irons, 

RIVETS. 

Diam.  of  rivets  for  shell  f  inch,  pitch  2$  ins. 
Do.     do.  heads  f  inch,  pitch  2}  ins. 

Do.     do.  connections  £  inch,  pitch  if  ins. 


WEIGHTS. 


Plate   XIL 


i 

TV 
TV 
i 


inch.      Wrought-iron, 
Cast-iron,     . 
Tubes,  brass, 
Total  weight  of  boiler, 


22,213 
2,469  Ibs. 
2,665 


.     27,347  Ibs. 
Weight  of  fresli  water,  6  inches  above  tubes,     13,060  Ibs. 


TUBES. 


Number,     . 
Outside  diameter, 
Thickness, 
Length,      . 


Grate- surf  ace,  one  boiler, 

Heating-surface,  one  boiler, 
Calorimeter,  one  boiler, 


32.00  sq.  ft.      Ratio  of  grate  to  heating-surface, 
821.80  sq.  ft.  calorimeter  to  grate-surface  , 

4.52  sq.  ft. 


.     1 66. 

2-J-  inches. 
.  No.  13  W.  G. 
6  feet  3  inches. 

i  to  25.6 
i  to  7.1 


©  © 


Plate  XIII. 


o 
m 

H 

> 

r 

CO 

o 

•n 


m 
H 

z 

0 

O 
•TI 

09 
O 

r 
m 


c 

• 

CO 
CO 


CO 

q 


Plate  XIV. 


TWO  BOILERS  FOR  S.  S.  "LORD  OF  THE  IS 


DESIGNED    BY    ADAM    MILLER,    LONDON,    1879. 


Area  of  grate-surface, 
Number  of  tubes, 
Diameter  of  safety-valve, 
Working  pressure,     . 


171  sq.  ft. 
780. 

Si  ins. 

75  H>s. 


Longitudinal  seams  of  boiler-shell  fitted  with  triple-riveted  butt-straps,  each  \ 
i  inch  diameter,  4-^  inches  pitch  ;  holes  drilled  after  plates  are  bent.  Circumfere 
riveted,  lap-jointed  ;  rivets  -J-f  inch  diameter,  3^  inches  pitch  ;  holes  in  inner  stra 
bending,  and  those  in  outer  strakes  drilled  when  in  place. 

Longitudinal  seams  of  superheater  fitted  with  triple- riveted  butt-straps,  each  • 
inch  diameter,  4^  inches  pitch  ;  holes  drilled  after  plates  are  bent.     Circumfere 
riveted,  lap-jointed  ;  rivets  i-j^  inches  diameter,  3^  inches  pitch  ;  holes  punched 
boiler-shell. 

Stay-tubes  4  inches  diameter,  f  inch  thick,  with  thread  cut  into  the  body  of  stay, 
diameter  of  3  inches. 


Jj_ 


oooooooo 

OOOOOOO 


ooooooo 
ooooooo 


ooooooooo 

OQOQQOQQQ 

oodooOooTd 

oooO 


Heating-surface,  tubes, 
plates, 
superheatei 
Total  heating-surface, 


Scale: 


.IS." 


Plate  XV 


[,786.88  sq.  ft. 
1,176.00  sq.  ft. 
616.00  sq.  ft. 

;c7888sd     ft                    =  

BUTT  JOIST  FOE 
1                                                               BOILER  SHELL. 

—  —  J  f>                       rs  —  1  —  rr~  

thick  ;  rivets 
seams  double- 
anched  before 

thick  ;  rivets 
seams  double- 
rilled  same  as 

ngan  effective 
i 

,„< 

/€   o      o      oto      o      o      o 
o         o     o     o     o     o     o 
o  lo     o      o  .LO      o      o      o 

o 

0 

i 

O    O        O        O  *T^D        O        O        o 

o          o      o      o     o      o      o 
\  o   o      o     o      o      o      o      o 

0 

<J 

"  n 

r 

C 

BUTT  JOINT  FOR 
SUPERHEATER. 

- 

1 

< 

\ 

1 

1 

.  * 

i 

— 

^"b    ooo      oTo      o      oo 

O]        OOoOoOO 

olo     o     o     cio     o     o     o 

cj  o     o     o     o*f=o      " 
-^5-4     o     o     o     o     o     o     c 
.^~  i  o     o     o     oLo     o     o     p 

ft 

1 

1 

\ 

l  M 

; 

r 

^S 

Feet. 


Grate-surface  -  4.75  sq.  ft. 
Heating  «  --119       " 
Calorimeter — .916      » 
IVeigTit  of  toiler  3100  Jbs. 
«       «  water  900 


BOILER  FOR  8*  X  8'  EN 


5NE,  U.  S.  S.  CUTTERS. 


Plate  XVI. 


THE 

R 

OF 


-- 


.        n 


ooooo  ooooo 
ooooo  ooooo 
ooooo  ooooo 
ooooo  ooooo 

ooooo  ooooo 
ooooo  ooooo 
ooooo  ooooo 
ooooo  ooooo 


oo  ooo 
ooooo 
ooooo 
ooo  oo 


ooooo: 

OOOOO' 

o  o  o  o  b  j 

ooooo 


ooooo  ooooo 
ooooo  ooooo 
ooooo  ooooo 
ooooo  ooooo 


00000:00000 
ooooojo  oo  oo 

OOOOOiOOOOO 

OOOOOlpOOOO 
-38|->4P^B£- 

QOOOOjOOOOO 

00000:00000 
ooooolooooo 
ooooo!  ooooo 


o  oooo 
ooo  oo 
o  oooo 
ooooo 

ooooo 
ooooo 
ooooo 
ooooo 


ooooo 
ooooo 
ooooo 
ppoqq 

ooooo 
ooooo 
ooooo 
ooooo 


ooooo  o 

±.'OOOOO   O 

oooooio 
_oqoqo_q 

o  o  o  o  o  o 
_ ooooo  o 

!     OOOOOiO 

oojDqqiq 


Plate  XVII. 

TOILERS  FOR 
-"PLYMOUTH. 


Feet. 


OOOOOOi 

oooooooo 
oooooooo 

OOOOOOOOi 

oooooooo 

OOOOOOOOv 

oooooooo/ 
ooooooo  / 
OOOOOQ/J 


\ 


\ 


Plate  XVII. 


Section  through.  Centre  of  Boiler. 

13  -  6" 


4 

1 


I 


/ 


OF  THE 

UNIVERSITY 


CO 
37 

> 

o 

z 
o 

°n 
O 
7) 

CO 
O 

r 
m 

30 

c/> 

-n 

C 
0> 

• 

o> 

• 

•X 

v% 

T3 

r 
-< 


TH 


. 
( 


\ 


Plate  XVIII. 


: 


--fflfc  Je-  -e- 


r~f 

'Mfa         W7 

(D 

_ 

— 

T 
°l 

m 

'" 

f 
| 

V 
i  — 

1 

r  h  H  h  fj  hy-i  w  h^5; 
l^         1 

«, 

O 

m 

> 

r 
<s> 

•n 
O 
n 

oo 
O 

r 
m 


c 

• 

0) 

• 

0) 

• 
*s 

•\ 

•o 

r 


o 

c 

H 

I 


Plate  XIX. 


"-     ~* 

—  •  .  —  .  •  —  .  „  —  -  —                      —  •  ——  — 

""    i""~ 

i 

1 

. 

m 

j 

L-     .    . 

2-7"                                                              \ 

i 

1 

V 

2-10" 


Single  Shear 


Mean  of  44149  Hw.per" 


Sheared  at  9000 


No.l 


Sheared  at  8900 


No.2 


Sheared  at  WOO 


Sheared  at  9*00 


.62 


N0.4HIHH 


Jfcon  o/  39263 16».j)er 


Sfc«jred  at  12900 


Sheared  at  12900 


Sheared  at  13300 


/ 

\ 

_ 

Sheared  at  127S 

la 

.50 

Noj'l 
lOll 

11 

1 

Jfean  of  39553  H>s.p«r ' 


Sheared  at  18800 


No. 
13 


Sheared  at  19500 


No.14 


Sheared  at  19650 


No.  15 


Sheared  at  ISSOi 


No.  1C 


O/41SD8  »»p«r  ' 


Slieared  at  3C5M 


.90 


Jfean<!/-W708B>«.per   " 


Grand  Af«».  0/41033  Uis.per 


Double  Sliear 


Sheared  at  16175 


No.l 


Sheared  at  16800 


Sheared  at  10060 


Sheared  at  10400 


No.4 


1  I 


aeon  o/  77318  (6s..per  ° 
Double  Shear 


Sheared  at  25650 


No.7 


Sheared  at  23700 


No.8|[ 


Sheared  at  23600 


f 


Sheai 


Jfean  of  79536  i&s.per  °' 
Double  Shear 


' 

\ 

Sh 

z 

sored  at  36650 

No.13 

II 

V 

Sheared  at  39iOO 


.77 


DPOD1 


Mean  of  76789  lbs.per  "" 
Double  Shear 


Sheared  at  51600 


No.19 


Could  not  be  screwed  up  tightly,  therefore  weak. 
Sheared  at  i7650 


Kot  screwed  up  tightly. 
Sheared  at  4C300 


Mean  of  75293  Ibs.per  °" 
Double  Shear 


Grand  Mean  0/78030  Ws.per  °* 
Double  Shear 


/ 

\ 

2 

Sheared  at  & 

No.25 

D 


Sheared  at  61700 


No.26 


/ 

\ 

L 

B 

1 

?Aearcd  at  C 

3650 

111 

No.S7 

/ 

\ 

Shearing  Attachment 


i  i    i    i    !  I                          i 

i 

:    i       | 

Xo.5 


Sheared  at  MM 


•n    |  Xo.G 


Plate  XX. 


X 


Xo.ll 


Sheared  at  15750 


.«" 


S/tcar 


Ko.l7|l 

It 


OanmfaiUMO 


Experiments  on  Shearing  Wrought  Iron  Bolts, 

Conducted  at  the  Washington  Xary  Yard, 


CUtf  Engineer  Wm.  H.  Shock,   U.  8.  N. 


i  ;  I'^xo 


0.22 


i'.f.l.      ?,i.'L'l.«) 


No.28 


1.M 

I 


Xo.29 


Sheared  at  XTVO 


Xo.24 


Sheared  at  Stito 

Tl 


Xo.30 


D 


V 

X.                  !                   t 

1  i 

a 


Shearing  Attachment 

m 


Sheared  at  17575 


Xo.5 


Sheared  at  17GOO 


Sheared  at  24600 


f   JXo.ll 


.S4 




No.12 


andatlMM 


No.lC 


Sheared  at 'MM 


No.17 


.79 


No.  18 


Sheared  at  51300 


No.22 


•«•<•<  at  OM 


Xo.23 


Sheared  at  51375 


Xo.24 


No.28 


Sfenred  a/  63535 


Xo.20 


Sheared  at  C3500 


m 


L    U 


1 

1 

J 

1           1 

Fig.l. 
MARINE  FLUE  BOILER. 


0 


o 


Plate  XXI. 


\ 


Fig-  2. 
BOILER  FOR  U.  S.  S.  "SHOCKOKON." 


11-6- 


f 

5  J 

e 

•^ 

^ 

—  32  — 


Fig.  3. 
BOILER  FOR  U.  S.  S.  "MORSE." 


SMOKE  BOX  EM> 


METHODS  OF  SECURING  BOILER  TUBES. 

Fig-  I-  Fig.  2. 


Plate  XXII. 


Fig.  6. 
TWEDDELL'S  HYDRAULIC  TUBE  EXPANDER. 


Fig.  7. 
SELKIRK'S  TUBE  BEADER. 


E  xpe  rime  fit  i 
Tubes  before 


No.  5 

2 1150  Ibs. 


No.C 

12000  Ibs. 


Tvbes  after  exper/'»tcr' 


Scale: 


0         1         2 


N0.25&86 

8225  Ibs. 


14 100  Ibs. 


So.  6,13  d- 14,29  dt  30,41  it  42, 
are  in  accordance  with  the  i'.S.A'aval  Practice, 


Tubes  before  experiment  with  brass  femUes. 


No.31&32 

19450  Ibs. 


Tubes  after  experiment  with  brass  ferrule*. 


Brass  Tubes, 
with  iron  ferrules. 


Composition  nuts. 


Plate  XXIII. 


No.  23  £24 

28310  Ibs. 
-Mean 


fh  iron  ferrules, 


i  Inches. 


Prosser's  process. 


>"o.45&-4(» 


U 


Dudgeons  process. 


Experiments  conducted  at  the  Washington  Navy  Yard,  Jan,  1877, 
Chief  Engineer  W>n.H.*J,<,,-k.  J'.S.X. 


V; 

•- 

:       ' 

-UJi 

jfetnod 
of 
fastening 

JEW 

'1 

-. 

Strain 
in 

pounds 

1 

2.5    .!)"  '2.4*  ", 

Proaser 

/ran 

75 

2,«:.0 

2 

2.41    - 

•• 

" 

" 

SO200 

3 

• 

• 

2.15 

•• 

Dudgeon 

" 

n 

12750 

4 

" 

M 

UM 

•• 

" 

H 

,. 

1GOUO 

6 

« 

" 

LM 

. 

« 

.Vane 

70 

21150 

c 

" 

,. 

LM 

» 

Prosser 

« 

71 

12UUU 

; 

.< 

u 

• 

.. 

.< 

Iron 

u 

27500 

8 

-.-.•: 

. 

Dudoeon 

.. 

ti 

4GOOO 

a 

" 

_'.::! 

i 

« 

« 

72 

30300 

10 

« 

J.ll 

.. 

« 

M 

« 

3GOOO 

11 

.< 

LM 

« 

Prosaer 

« 

•• 

25300 

12 

.. 

.. 

« 

.. 

.. 

.. 

.. 

2G400 

11 

» 

" 

•• 

. 

A'./tj'U/ci 

.Vune 

75 

10450 

11 

M 

.. 

tt 

,i 

« 

" 

•• 

27000    ; 

15 

« 

« 

tt 

« 

« 

iron 

.. 

40150 

1C 

.. 

« 

« 

« 

« 

" 

.. 

JS600 

17 

"    .. 

.,    , 

, 

.. 

«*ooo 

U 

a 

a 

a 

a 

- 

21400 

19 

«t 

_ 

- 

M 

• 

Iron 

- 

3U30U 

20 

a 

- 

_>  ID 

U 

• 

ft 

- 

41050    , 

21 

S.( 

.9 

2.0" 

•• 

Dudgeon 

Acme 

c;.-, 

7050 

22 

- 

ft 

- 

- 

u 

• 

_ 

KIM 

23 

- 

- 

- 

- 

« 

/ron 

04V      14400 

-•! 

-• 

" 

" 

13SOO 

4  r 

>  £ 

V 

V 
2.5 

1=::^ 

Method 
of 

'•;  -'<  I  END 

A 

Strain 
pound* 

.'/ 

M 

Dudgeon 

.Vtwie 

- 

8100 

26 

•• 

-• 

.. 

M 

« 

« 

- 

8150 

27 

H 

-• 

" 

u 

" 

/ron 

- 

14250 

25 

•• 

.- 

.. 

M 

« 

" 

- 

14550 

90 

•  • 

« 

•< 

« 

Proaser 

Xune 

7*° 

14450 

10 

•• 

- 

.. 

.. 

•• 

•• 

M   1     150OO 

11 

- 

« 

•• 

M 

D    7  .'  • 

u 

«  1     1707* 

12 

« 

" 

•• 

•• 

" 

» 

21S2S 

U 

« 

.. 

.. 

M 

« 

Brass 

32250 

34 

• 

M 

« 

» 

M 

" 

"   1     11400 

30       .. 

•• 

M 

« 

JVo««er 

" 

227511 

36 

• 

.. 

« 

M 

« 

• 

22:iiu 

18 

„ 

B 

.1 

. 

" 

" 

70  !     17150 
..          17100 

1* 

N 

« 

" 

« 

Dudgeon 

« 

24SOO 

40 

« 

« 

.. 

« 

.. 

.. 

<. 

2JOOO 

41 

.. 

«. 

•• 

PW««r 

.Vane 

75 

1000 

42 

_ 

« 

- 

- 

« 

• 

_ 

111-50 

41 

« 

• 

_ 

- 

/•'    '.. 

- 

- 

IMM 

11 

w 

- 

- 

a 

« 

• 

a 

22250 

45 

a 

- 

~ 

_ 

- 

Brass 

-           2U5!*) 

46 

« 

- 

- 

- 

a 

a 

27550 

47 

« 

- 

_ 

- 

Pro5«er 

« 

.   1     15250 

45 

'• 

•• 

•JIC--50 

Tubes  bej 


No.  1 

29050  Ibs. 


No.  2 
19950  Ibs. 


No.  3 
2C900  Ibs. 


-^•^r—^-^f 


No.  4 
25525  Ibs. 


No.  5 
20250  Ibs. 
Tubes  < 


No.  11 

29TOO  Ibs. 


*NC5 

a: 


No.  12 

29650  Ibs. 


No.  13 
11300  Ibs. 


— i — ^_- 

n 


f  "  i 


No.  14 

14800  Ibs. 


r  "i  7  i" 


JZD 


No.  15 

8850  Ibs. 

Tubes  aj 


> 


_J 


*> r 

cr 


RUSSELL  A  STRUTHERS,  ENG'S,  N,Y. 


•  1-illlUlt. 


Plate  XXI V. 


Experiment  with  Iron  Tubes,  with  Copper,  Iron  &  Steel  tube  plates. 

Conducted  at  the  Washington  Navy  Tar<l,  Jan.  1877. 

by 

Chief  Engineer  Wm.  H.  Shod,  U.  S.  JV. 


No.  6 

17300  Ibs. 

experiment. 


No.  7 
20450  Ibs. 


No.  8 

24650  Ibs. 


_J 


No.  9 

22700  Ibs. 


No.  10 
21600  Ibs. 


No.  16 
5950  Ibs. 


Tubes  expanded  by 
Dudgeons  process. 


No.  17 

221 00  Ibs. 


Ins.  Ins.  Sq.in      Ins.  In. 

(  Copper  ring  in  Ion 

i      3'i    2';     .981    2'i       Iron   7-16    Steel.    X     1     tube-plalc.  Ends 

f     tube  nveted  over. 


ring  in  lower  i 
'off 


., 

" 

" 

" 

"    Riveted  over. 

::  :: 

Copp-     ?* 

„ 

29-16 

.4 

Steel.    H    Partly  riveted. 

"          "    Tron  femilcs. 

::  .. 
.,  . 

- 

'*•• 

K 

'*•  Simply  expanded, 
i  Tube-plate  boles    ta-  / 

.,  .. 

29-16 

K 

• 

i  Tube-plate    holes  ta-  ) 
"     -        per  2*h  '  -213-16' 
;  (        and  25i-    •  29-16 

39050 

IW501 
20900 

25525 

302^0 

17330 


8850 

"     .    595° 

71°         22100 


Plate  XXY. 


Scum  Pipe 


33 

Z 

m 

oo 
o 


m 

X) 

00 

«< 

H 


I 
O 

> 

•J) 
0 


td 


Plate  XXVI. 


rr  ? 


m 

•u 
m 


H  3 

C  <?» 

oo  r 

C 


CO 

O 

r 
m 


Fig.l. 
THE  HERRESHOFF  COIL  BOILER. 


Plate  XXVII. 


i 


IJJPTJPJCT   l  T 

N  ii*  i  I 

ijiiiiij     if  i1— ' 

'i    >l    j      i'     '.!  i     !   i  i!     ! 

I  •         i        i 

HNL  JF 


Fig.  2. 
THE  BELLEVILLE  BOILER. 


Pig.  i.  Plate  XXVIII. 

BOILER  FOR  8X8  ENGINE,  U.  S.  S.  CUTTERS. 


Grate-surface-5  .33  sq.ft . 
Steam-Room-4.10  cub.ft. 


Heating-surface-150  sq.ft. 
Weight  of  Boller-2110  Ibs. 

33=0: 


Fig.  2. 
THE  DAVEY-PAXM AN  BOILER. 


42 


Plate  XXIX. 


CD 


1  m 

30 

V)  8° 

O  "H 
TI  C 

<=! 


co 

'„  a 

z  ° 

±  o 

T3   30 
GO   00 

o  -n 


f_     v 


OF  THE 

UNIVERSITY 

cr 


^^_ 


Plate  XXX. 


U.  S.  S."NIPSIC". 

12    «    0          1         2         3         4         5 

Scale:   litiiilmui        I        I    =1=          E3  Teet, 


J.A.H. 


15" 


Plate  XXXI. 


^ 

1  \ 
-if 



' 

_ 


_- 


Rnr 


Tig.  3. 


Fig.  4 


Plate  XXXII. 


STEAM  STOP  VALVES  &  FEED 

VALVE%FOR  BOILERS  OF 

U.  S.  S.  "NIPSIC." 


rig.  2.  i 


c    _*_„. ;_  _:!j  — 


/    .^--.^ 

'  /f  ^\v\ 

,  ^Ky>hv 

^f^7  \ 

^  KX 


UJ-1 


Plate  XXXIII. 


•H 
m 

73 

O 

> 

c 

O 

m 

•n 
O 
so 

CD 
O 

r 
m 


O 
-n 

C 


O 


Plate  XXXIV. 


Fig.l. 

SAFETY  VALVE  FOR  BOILERS, 
U.  S.  S.  "NIPSIC. 


Fig.  2. 

SAFETY  VALVE  APPROVED   BY   THE 
BOARD  OF  SUPERVISING  INSPECTORS  OF  STEAM-VESSELS. 


Fig.3. 
ASHCROFT'S  SAFETY  VALVE. 


Kg.l. 

KOERTING'S  JET  APPARATUS. 


Plate  XXXY. 


SELLERS'  SELF-ADJUSTING  INJECTOR. 


^ 


rig.  3. 

KOERTING'S  UNIVERSAL 
LIFTING  INJECTOR. 


gu'iiiu.    '  •  *-\ 


Water 


Plate  XXXYI. 


SPECIMENS  OF  RIVETS  AND  RIVET-HEADS 

FROM  BOILERS  OF  COPPER-ROLLING  MILL, 

NAVY  YARD,  WASHIKGTOIf,  D.  C.  1879. 


- 


YE.  01 143 


£  • 


• 

.   -  • 


/.      .  ••*%&.  A 


^ 

_< 


• 


.    . 

.* 

'    •  • 


• 


, 


f 

; 


» 

•••     *. 


-^ 


'   <•• 


€•   '** 

1  , 


\       , 


•   '    ,     : 


^»->  .  I 

^ 


'>*        - 

^     ^ 


